@ Northeastern University        COE | ECE | MIE
Research Group of Prof. Yongmin Liu
   Home
   Research
   Publications
   Members
   News
   Opening
   Contact

Publication Statistics (from Researcher ID)
Total citations: >1600
H-index: 20

 
Selected Journal Publications
– H. Cang, Y. M. Liu, Y. Wang, X. Yin, and X. Zhang, "Giant suppression of photobleaching for single molecule detection via the Purcell effect", Nano Letters 13, 5945 (2013) [PDF]
– C. L. Zhao*, Y. M. Liu*, Y. H. Zhao, N. Fang, and T. J. Huang, "A reconfigurable plasmofluidic lens", Nature Communications 4:2350 (2013) [PDF]
– Y. M. Liu*, S. Palomba*, Y. Park, T. Zentgraf, X. B. Yin and X. Zhang, "Compact magnetic antennas for directional excitation of surface plasmons", Nano Letters 12, 4853 (2012) [PDF]
– Y. M. Liu and X. Zhang, "Recent advances in transformation optics" (invited review paper), Nanoscale 4, 5277 (2012) [PDF]
– S. C. Kehr*, Y. M. Liu*, L. W. Martin, P. Yu, M. Gajek, S.-Y. Yang, C.-H. Yang, M. T. Wenzel, R. Jacob, H.-G. von Ribbeck, M. Helm, X. Zhang, L. M. Eng and R. Ramesh, "Near-field examination of perovskite-based superlenses and superlens-enhanced probe-object coupling", Nature Communications 2, 249 (2011) [PDF]
– T. Zentgraf*, Y. M. Liu*, M H. Mikkelsen*, J. Valentine and X. Zhang, "Plasmonic Luneburg and Eaton lenses", Nature Nanotechnology 6, 151 (2011) [PDF]
– Y. M. Liu and X. Zhang, "Metamaterials: a new frontier of science and technology" (invited review paper), Chemical Society Reviews 40, 2494 (2011) [PDF]
– H. Cang, A. Labno, C. G. Lu, X. B. Yin, M. Liu, C. Glandden, Y. M. Liu and X. Zhang, "Probing the electromagnetic field of a 15-nanometre hotspot by single molecule imaging", Nature 469, 385 (2011) [PDF]
– Y. M. Liu, T. Zentgraf, G. Bartal and X. Zhang, "Transformational plasmon optics", Nano Letters 10, 1991(2010) [PDF]. See News and Views by Nature Nanotechnlogy.
– M. Liu, T. Zentgraf, Y. M. Liu, G. Bartal and X. Zhang, "Light-driven nanoscale plasmonic motors", Nature Nanotechnology 5, 570 (2010) [PDF]. See Research Hilight by Nature, and News and Views by Nature Nanotechnlogy.
– J. Yao*, Z. W. Liu*, Y. M. Liu*, Y. Wang, C. Sun, G. Bartal, A. Stacy and X. Zhang, "Optical negative refraction in bulk metamaterials of nanowires", Science 321, 930 (2008) [PDF]. Ranked among Top 10 Scientific Discoveries and 50 Best Inventions of 2008 by TIME magazine, and Top 100 Stories of 2008 by DISCOVER magazine.
– Y. M. Liu, G. Bartal, D. A. Genov and X. Zhang, "Subwavelength discrete solitons in nonlinear metamaterials", Physical Review Letters 99, 153901 (2007) [PDF]. See Research Highligh by Nature Photonics.

Full List of Journal Publications
[42] C. L. Zhao, Y. M. Liu, J. Yang and J. S. Zhang, "Single-molecule detection and radiation control in solutions at high concentrations via a heterogeneous optical slot antenna", Nanoscale 6, 9103 (2014) [PDF]

We designed a heterogeneous optical slot antenna (OSA) that is capable of detecting single molecules in solutions at high concentrations, where most biological processes occur. A heterogeneous OSA consists of a rectangular nanoslot fabricated on heterogeneous metallic films formed by sequential deposition of gold and aluminum on a glass substrate. The rectangular nanoslot gives rise to large field and fluorescence enhancement for single molecules. The near-field intensity inside a heterogeneous OSA is 170 times larger than that inside an aluminum zero-mode waveguide (ZMW), and the fluorescence emission rate of a molecule inside the heterogeneous OSA is about 70 times higher than that of the molecule in free space. Our results can be used as a direct guidance for designing high-performance, low-cost plasmonic nanodevices for the study of bio-molecule and enzyme dynamics at the single-molecule level.

[41] K, Yao, H. Y. Chen, Y. M. Liu, and X. Y. Jiang, "An analogy strategy for transformation optics", New Journal of Physics 16, 063008 (2014) [PDF]

We introduce an analogy strategy to design transformation optical devices. Based on the similarities between field lines in different physical systems, the trajectories of light can be intuitively determined to curve in a gentle manner, and the resulting materials are isotropic and nonmagnetic. Furthermore, the physical meaning of the analogue problems plays a key role in the removal of dielectric singularities. We illustrate this approach by creating two designs of carpet cloak and a collimating lens as representative examples in two- and three dimensional spaces, respectively. The analogy strategy reveals the intimate connections between different physical disciplines, such as optics, fluid mechanics and electrostatics.

[40] Y. H. Cao, J. Xie, Y. M. Liu, and Z. Y. Liu, "Modeling and optimization of photonic crystal devices based on transformation optics method", Optics Express 22, 2725 (2014) [PDF]
[39] K. Yao and Y. M. Liu, "Plasmonic Metamaterials", Nanotechnology Review 3, 177 (2014) [PDF]

Plasmonics and metamaterials have attracted considerable attention over the past decade, owing to the revolutionary impacts that they bring to both the fundamental physics and practical applications in multiple disciplines. Although the two fields initially advanced along their individual trajectories in parallel, they started to interfere with each other when metamaterials reached the optical regime. The dynamic interplay between plasmonics and metamaterials has generated a number of innovative concepts and approaches, which are impossible with either area alone. This review presents the fundamentals, recent advances, and future perspectives in the emerging field of plasmonic metamaterials, aiming to open up new exciting opportunities for nanoscience and nanotechnology.


[38] H. Cang, Y. M. Liu, Y. Wang, X. Yin, and X. Zhang, "Giant suppression of photobleaching for single molecule detection via the Purcell effect", Nano Letters 13, 5945 (2013) [PDF]

We report giant suppression of photobleaching and a prolonged lifespan of single fluorescent molecules via the Purcell effect in plasmonic nanostructures. The plasmonic structures enhance the spontaneous emission of excited fluorescent molecules, reduce the probability of activating photochemical reactions that destroy the molecules, and hence suppress the bleaching. Experimentally, we observe up to a 1000-fold increase in the total number of photons that we can harvest from a single fluorescent molecule before it bleaches. This approach demonstrates the potential of using the Purcell effect to manipulate photochemical reactions at the subwavelength scale.

[37] Y. M. Liu and X. Zhang, "Metasurfaces for manipulating surface plasmons", Appled Physics Letters 103, 141101 (2013) [PDF]

Metasurfaces have recently emerged as an innovative approach to control light propagation with unprecedented capabilities. Different from previous work concentrating on steering far-field propagating waves, here we demonstrate that metallic metasurfaces can efficiently and effectively manipulate surface plasmons in the near-field regime. By engineering the dispersion of surface plasmons on a simple grating structure, we are able to realize normal, non-divergent as well as anomalous diffraction of surface plasmons. In particular, all-angle and broadband negative refraction of surface plasmons is achieved, largely attributed to the uniquely designed hyperbolic constant frequency contour of surface plasmons propagating along the metasurface.

[36] C. L. Zhao*, Y. M. Liu*, Y. H. Zhao, N. Fang, and T. J. Huang, "A reconfigurable plasmofluidic lens", Nature Communications 4:2305 (2013) [PDF]

The majority of plasmonic devices are in the solid state and have limited tunability or configurability. Moreover, individual solid-state plasmonic devices lack the ability to deliver multiple functionalities. Here we utilize laser-induced surface bubbles on a metal film to demonstrate, for the first time, a plasmonic lens in a microfluidic environment. Our 'plasmofluidic lens' is dynamically tunable and reconfigurable. We record divergence, collimation and focusing of surface plasmon polaritons using this device. Our results show that the integration of plasmonics and microfluidics allows for new opportunities in developing complex plasmonic elements with multiple functionalities, high-sensitivity and high-throughput biomedical detection systems, as well as on-chip, all-optical information processing techniques.

[35] Y. M. Liu*, S. Palomba*, Y. Park, T. Zentgraf, X. B. Yin and X. Zhang, "Compact magnetic antennas for directional excitation of surface plasmons", Nano Letters 12, 4853 (2012) [PDF]

Bridging the optical antenna theory and the recently developed concept of metamaterials, we demonstrate a subwavelength, highly efficient plasmonic source for directional generation of surface plasmon polaritons (SPPs). The designed device consists of two nanomagnetic resonators with detuned resonant frequencies. By tailoring the relative phase at resonance and the separation between the two nanoresonators, SPPs can be steered to predominantly propagate along one specific direction. This novel magnetic nanoantenna paves a new way to manipulate photons in the near-field, and also could be useful for SPP-based nonlinear applications, active modulations, and wireless optical communications.

[34] Y. M. Liu and X. Zhang, "Recent advances in transformation optics" (invited review paper), Nanoscale 4, 5277 (2012) [PDF]

Within the past a few years, transformation optics has emerged as a new research area, since it provides a general methodology and design tool for manipulating electromagnetic waves in a prescribed manner. In this paper, we review the most recent advances in transformation optics. We focus on the theory, design, fabrication and characterization of transformation devices such as the carpet cloak, "Janus" lens and plasmonic cloak at optical frequencies, which allow routing light at the nanoscale. We also provide an outlook of the challenges and future directions in this fascinating area of transformation optics.

[33] R. H. Fan, R. W. Peng, X. R. Huang, J. Li, Y. M. Liu, Q. Hu, M. Wang and X. Zhang, "Transparent metals for ultrabroadband electromagnetic waves", Advanced Materials 24, 1980 (2012) [PDF]
[32] S. C. Kehr, P. Yu, Y. M. Liu, M. Parzefall, A. I. Khan, R. Jacob, M. T. Wenzel, H.-G. von Ribbeck, M. Helm, X. Zhang, L. M. Eng and R. Ramesh, "Microspectroscopy on perovskite-based superlenses", Optical Materials Express 1, 1051 (2011) [PDF]
[31] P. Zhang*, S. Wang*, Y. M. Liu*, X. B. Yin, C. G. Lv, Z. G. Chen and X. Zhang, "Plasmonic Airy beams with dynamically controlled trajectories", Optics Letters 36, 3191 (2011) [PDF]
[30] M. Gharghi, C. Gladden, T. Zentgraf, Y. M. Liu, X. B. Yin, J. Valentine and Xiang Zhang, "A carpet cloak for visible light", Nano Letters 11, 2825 (2011) [PDF]

We report an invisibility carpet cloak device, which is capable of making an object undetectable by visible light. The cloak is designed using quasi conformal mapping and is fabricated in a silicon nitride waveguide on a specially developed nanoporous silicon oxide substrate with a very low refractive index (n<1.25). The spatial index variation is realized by etching holes of various sizes in the nitride layer at deep subwavelength scale The fabricated device demonstrates wideband invisibility throughout the visible spectrum with low loss. This silicon nitride on low index substrate can also be a general scheme for implementation of transformation optical devices at visible frequencies.

[29] S. C. Kehr*, Y. M. Liu*, L. W. Martin, P. Yu, M. Gajek, S.-Y. Yang, C.-H. Yang, M. T. Wenzel, R. Jacob, H.-G. von Ribbeck, M. Helm, X. Zhang, L. M. Eng and R. Ramesh, "Near-field examination of perovskite-based superlenses and superlens-enhanced probe-object coupling", Nature Communications 2, 249 (2011) [PDF]

We demonstrate a superlens for electric evanescent fields with low losses using perovskites in the mid-infrared regime. The combination of near-field microscopy with a tunable free-electron laser allows us to address precisely the polariton modes, which are critical for super-resolution imaging. We spectrally study the lateral and vertical distributions of evanescent waves around the image plane of such a lens, and achieve imaging resolution of λ/14 at the superlensing wavelength. Interestingly, at certain distances between the probe and sample surface, we observe a maximum of these evanescent fields. Comparisons with numerical simulations indicate that this maximum originates from an enhanced coupling between probe and object, which might be applicable for multifunctional circuits, infrared spectroscopy and thermal sensors.

[28] T. Zentgraf*, Y. M. Liu*, M H. Mikkelsen*, J. Valentine and X. Zhang, "Plasmonic Luneburg and Eaton lenses", Nature Nanotechnology 6, 151 (2011) [PDF]

We use grey-scale lithography to adiabatically tailor the topology of a dielectric layer adjacent to a metal surface to demonstrate a plasmonic Luneburg lens that can focus surface plasmon polaritons. We also make a plasmonic Eaton lens that can bend surface plasmon polaritons. Because the optical properties are changed gradually rather than abruptly in these lenses, losses due to scattering can be significantly reduced in comparison with previously reported nano plasmonic devices. Our approach opens a new way to achieve low-loss, functional plasmonic elements with a standard fabrication technology based on grey-scale electron-beam lithography and is fully compatible with active plasmonics. Furthermore, this method provides a scheme with which to realize more complex two-dimensional plasmonic elements using transformation optics.

[27] Y. M. Liu and X. Zhang, "Metamaterials: a new frontier of science and technology" (invited review paper), Chemical Society Reviews 40, 2494 (2011) [PDF]

This critical review focuses on the fundamentals, recent progresses and future directions in the research of electromagnetic metamaterials. An introduction to metamaterials followed by a detailed elaboration on how to design unprecedented electromagnetic properties of metamaterials is presented. A number of intriguing phenomena and applications associated with metamaterials are discussed, such as negative refraction, sub-diffraction-limited imaging, strong optical activities in chiral metamaterials, interaction of meta-atoms and transformation optics. Finally, we offer an perspective of metamaterials research including 3D optical metamaterials, nonlinear metamaterials and "quantum" perspectives of metamaterials.

[26] X. D. Yang, Y. M. Liu, R. F. Oulton, X. B. Yin and X. Zhang, "Optical forces in hybrid plasmonic waveguides", Nano Letters 11, 321 (2011) [PDF]

We demonstrate that in a hybrid plasmonic system the optical force exerted on a dielectric waveguide by a metallic substrate is enhanced by more than 1 order of magnitude compared to the force between a photonic waveguide and a dielectric substrate.. Moreover, the hybridization between the surface plasmon modes and waveguide modes allows efficient optical trapping of single dielectric nanoparticle with size of only several nanometers in the gap region, manifesting various optomechanical applications such as nanoscale optical tweezers.

[25] H. Cang, A. Labno, C. G. Lu, X. B. Yin, M. Liu, C. Glandden, Y. M. Liu and X. Zhang, "Probing the electromagnetic field of a 15-nanometre hotspot by single molecule imaging", Nature 469, 385 (2011) [PDF]
[24] C. W. Chang, M. Liu, S. Nam, S. Zhang, Y. M. Liu, G. Bartal and Xiang Zhang, "Optical Möbius symmetry in metamaterials", Physical Review Letters 105, 235501 (2010) [PDF]
[23] Y. M. Liu*, S. Wang*, Y. Park*, X. B. Yin and X. Zhang, "Fluorescence enhancement by a two-dimensional dielectric annular Bragg resonant cavity", Optics Express 18, 25029 (2010) [PDF]
[22] Y. M. Liu, T. Zentgraf, G. Bartal and X. Zhang, "Transformational plasmon optics", Nano Letters 10, 1991(2010) [PDF]

Taking advantage of transformation optics, we demonstrate that the confinement as well as propagation of surface plasmons can be managed in a prescribed manner by careful control of the dielectric material properties adjacent to a metal. Since the metal properties are completely unaltered, it provides a straightforward way for practical realizations. We show that our approach can assist to tightly bound SPPs over a broad wavelength band at uneven and curved surfaces, where SPPs would normally suffer significant scattering losses. In addition, a plasmonic waveguide bend and a plasmonic Luneburg lens with practical designs are proposed.

[21] M. Liu, T. Zentgraf, Y. M. Liu, G. Bartal and X. Zhang, "Light-driven nanoscale plasmonic motors", Nature Nanotechnology 5, 570 (2010) [PDF]

Photons have both linear and angular momentum. The transfer of linear momentum from photons to an object results in an optical force that can be used for optical trappingand cooling. Also, the angular momentum carried by photons can induce a mechanical torque via scattering or absorbance. The ability to generate strong rotational force at the nanoscale could open up a range of applications in physics, biology and chemistry, including DNA unfolding and sequencing and nanoelectromechanical systems. Here, we demonstrate a nanoscale plasmonic structure that can, when illuminated with linearly polarized light, generate a rotational force that is capable of rotating a silica microdisk that is 4,000 times larger in volume. Furthermore, we can control the rotation velocity and direction by varying the wavelength of incident light to excite different plasmonic modes.

[20] S. Zhang, Y. S. Park, Y. M. Liu, T. Zentgraf and X. Zhang, "Far-field measurement of ultra-small plasmonic mode volume", Optics Express 18, 6048 (2010) [PDF]
[19] Y. Gao, J. P. Huang, Y. M. Liu, L. Gao, K. W. Yu and X. Zhang, "Optical negative refraction in ferrofluids with magnetocontrollability", Physical Review Letters 104, 034501 (2010) [PDF]
[18] H. Liu, Y. M. Liu, T. Li, S. M. Wang, S. N. Zhu and X. Zhang, "Coupled magnetic plasmons in metamaterials" (invited review paper), Physica Status Solidi B 246, 1397 (2009) [PDF]
[17] J. Yao*, Z. W. Liu*, Y. M. Liu*, Y. Wang, C. Sun, G. Bartal, A. Stacy and X. Zhang, "Optical negative refraction in bulk metamaterials of nanowires", Science 321, 930 (2008) [PDF]

Photons have both linear and angular momentum. The transfer of linear momentum from photons to an object results in an optical force that can be used for optical trappingand cooling. Also, the angular momentum carried by photons can induce a mechanical torque via scattering or absorbance. The ability to generate strong rotational force at the nanoscale could open up a range of applications in physics, biology and chemistry, including DNA unfolding and sequencing and nanoelectromechanical systems. Here, we demonstrate a nanoscale plasmonic structure that can, when illuminated with linearly polarized light, generate a rotational force that is capable of rotating a silica microdisk that is 4,000 times larger in volume. Furthermore, we can control the rotation velocity and direction by varying the wavelength of incident light to excite different plasmonic modes.

[16] Y. M. Liu, G. Bartal and X. Zhang, "All-angle negative refraction and imaging in a bulk medium made of metallic nanowires in the visible region", Optics Express 16, 15439 (2008) [PDF]
[15] Y. M. Liu, G. Bartal, D. A. Genov and X. Zhang, "Subwavelength discrete solitons in nonlinear metamaterials", Physical Review Letters 99, 153901 (2007) [PDF]

We present the first study of subwavelength discrete solitons in nonlinear metamaterials: nanoscaled periodic structures consisting of metal and nonlinear dielectric slabs. The solitons supported by such media result from a balance between tunneling of surface plasmon modes and nonlinear self-trapping. The dynamics in such systems, arising from the threefold interplay between periodicity, nonlinearity, and surface plasmon polaritons, is substantially different from that in conventional nonlinear dielectric waveguide arrays. We expect these phenomena to inspire fundamental studies as well as potential applications of nonlinear metamaterials, particularly in subwavelength nonlinear optics.

[14] H. Liu, D. A. Genov, D. M. Wu, Y. M. Liu, Z. W. Liu, C. Sun, S. N. Zhu and X. Zhang, "Magnetic plasmon hybridization and optical activity at optical frequencies in metallic nanostructures", Physical Review B 76, 073101 (2007) [PDF]
[13] R. F. Oulton, D. F. P. Pile, Y. M. Liu and X. Zhang, "Scattering of surface plasmon polaritons at abrupt surface interfaces: Implications for nanoscale cavities", Physical Review B 76, 035408 (2007) [PDF]
[12] W. Wu, E. Kim, E. Ponizovskaya, Y. M. Liu, Z. N. Yu , N. Fang, Y. R. Shen, A. M. Bratkovsky, W. Tong, C. Sun, X. Zhang , S. Y. Wang and R. S. Williams, "Optical metamaterials at near and mid-IR range fabricated by nanoimprint lithography", Applied Physics A 87, 143 (2007) [PDF]
[11] W. Wu*, Y. M. Liu*, E. Kim*, Z. N. Yu, N. Fang, C. Sun, X. Zhang, Y. R. Shen, S. Y. Wang and R. S. Williams, "Midinfrared metamaterials fabricated by nanoimprint lithography", Applied Physics Letters 90, 063107(2007) [PDF]

A metamaterial comprising an ordered array of four metallic L-shaped components designed to operate in the mid-IR frequency regime has been fabricated and characterized. The fourfold rotational symmetry of the unit cell should suppress the undesirable bianisotropy observed for split-ring resonators. Nanoimprint lithography was used to demonstrate scalability for mass production. A dipole plasmon resonance with a negative permittivity and a magnetic resonance with a negative permeability were observed at wavelengths of 3.7 and 5.25 micro-meter, respectively, in agreement with theoretical predictions.

[10] Y. M. Liu, N. Fang, C. Sun and X. Zhang, "Symmetric and antisymmetric modes of electromagnetic resonators", Applied Physics A 87, 171 (2007) [PDF]
[9] H. Liu, D. A. Genov, D. M. Wu, Y. M. Liu, J. M. Steele, C. Sun, S. N. Zhu and X. Zhang, "Magnetic plasmon propagation along a chain of connected subwavelength resonators at infrared frequencies", Physical Review Letters 97, 243902 (2006) [PDF]
[8] X. F. Hu, Z. H. Peng, R. W. Peng, Y. M. Liu, F. Qiu, X. Q. Huang, A. Hu and S. S. Jiang, "Electronic delocalization and persistent currents in nonsymmetric-dimer mesoscopic rings threaded by magnetic flux", Journal of Applied Physics 95, 7545 (2004) [PDF]
[7] R. W. Peng, Y. M. Liu, X. Q. Huang, M. Wang, A. Hu, S. S. Jiang, D. Feng, L. Z. Ouyang and J. Zou, "Dimerlike positional correlation and resonant transmission of electromagnetic waves in aperiodic dielectric multilayers", Physical Review B 69, 165109 (2004) [PDF]
[6] X. Q. Huang, S. S. Jiang, R. W. Peng, Y. M. Liu, F. Qiu and A. Hu, "Characteristic wavefunctions of one-dimensional periodic, quasiperiodic and random lattices", Modern Physics Letters B 17, 1461 (2003) [PDF]
[5] F. Qiu, R. W. Peng, X. Q. Huang, Y. M. Liu, M. Wang, A. Hu and S. S. Jiang, "Resonant transmission and frequency trifurcation of light waves in Thue-Morse dielectric multilayers", Europhysics Letters 63, 853 (2003) [PDF]
[4] R. W. Peng, X. Q. Huang, F. Qiu, Y. M. Liu, A. Hu and S. S. Jiang, "Structural symmetry and optical properties of dielectric multilayers", Surface Review and Letters 10, 311 (2003) [PDF]
[3] Y. M. Liu, R. W. Peng, X. Q. Huang, M. Wang, A. Hu and S. S. Jiang, "Resonant scattering in random polymer chains with inversely symmetric impurities", Physical Review B 67, 205209 (2003) [PDF]
[2] Y. M. Liu, R. W. Peng, X. Q. Huang, M. Wang, A. Hu and S. S. Jiang, "Absence of suppression in the persistent current by delocalization in random-dimer mesoscopic rings", Journal of the Physical Society of Japan 72, 346 (2003) [PDF]
[1] Y. M. Liu, R. W. Peng, G. J. Jin, X. Q. Huang, M. Wang, A. Hu and S. S. Jiang, "Persistent currents in k-component Fibonacci mesoscopic rings threaded by a magnetic flux", Journal of Physics: Condensed Matter 14, 7253 (2002) [PDF]
*First authors with equal contributions.

Please note that all of the PDF files linked in this page are copyrighted. They are provided for your convenience, while you can download them only if you are entitled to do so by the corresponding publishers.

Copyright©Yongmin Liu's Research Group