(8–6-07) BOSTON, Mass. North­eastern Uni­ver­sity Physics pro­fessor Sergey V. Kravchenko along with col­leagues Svet­lana Anis­si­mova (North­eastern Uni­ver­sity), A Pun­noose (City Col­lege if the City Uni­ver­sity of New York), AM Finkel­stein (Weiz­mann Insti­tute of Sci­ence, Israel) and TM Klap­wijk (Delft Uni­ver­sity of Tech­nology, Nether­lands), has pub­lished an impor­tant new paper in the August issue of Nature Physics which answers a long standing ques­tion in the field of con­densed matter physics.

The dis­covery of the metal-​​insulator tran­si­tion (MIT) in two-​​dimensional elec­tron sys­tems by Kravchenko and col­leagues in 1994 chal­lenged the veracity of one of the most influ­en­tial con­jec­tures in the physics of dis­or­dered elec­trons by Abra­hams, Anderson, Lic­cia­rdello and Ramakr­ishnan (1979) which stated that “in two dimen­sions, there is no true metallic behavior.”

How­ever, the 1979 theory did not account for inter­ac­tions between elec­trons. In this new paper, Kravchenko and col­leagues inves­ti­gate the inter­play between the electron-​​electron inter­ac­tions and dis­order near the MIT using simul­ta­neous mea­sure­ments of elec­trical resis­tivity and magnetoconductance.

The researchers show that both the resis­tance and inter­ac­tion ampli­tude exhibit a fan-​​like spread as the MIT is crossed. From this data, the researchers have con­structed a resistance-​​interaction flow dia­gram of the MIT that clearly reveals a quantum crit­ical point, as pre­dicted by the recent two-​​parameter scaling theory by two of the authors (A. Pun­noose and A.M. Finkel­stein). The metallic side of this dia­gram is accu­rately described by the renormalization-​​group theory without any fit­ting para­me­ters. In par­tic­ular, the metallic tem­per­a­ture depen­dence of the resis­tance sets in when the inter­ac­tion ampli­tude reaches a value in remark­able agree­ment with the one pre­dicted by theory.

To the best of our knowl­edge, this is the first obser­va­tion of the tem­per­a­ture depen­dence of the strength of the electron-​​electron inter­ac­tions,” said Kravchenko. “We found that the inter­ac­tion grows in the metallic phase as the tem­per­a­ture is reduced and is sup­pressed in the insu­lating phase.”

Whether or not the elec­trons can con­duct in two dimen­sions at very low tem­per­a­tures is a ques­tion that has been hotly debated for more than a decade,” said Kravchenko. “We now know that, because of the inter­ac­tions between them, they can, and we have a theory that quan­ti­ta­tively and qual­i­ta­tively explains things.”

An advance copy of the paper is avail­able online at: http://​www​.nature​.com/​n​p​h​y​s​/​i​n​d​e​x​.​h​tml

About Nature Physics:

Nature Physics pub­lishes papers of the highest quality and sig­nif­i­cance in all areas of physics, pure and applied. The journal con­tent reflects core physics dis­ci­plines, but is also open to a broad range of topics whose cen­tral theme falls within the bounds of physics. The­o­ret­ical physics, par­tic­u­larly where it is per­ti­nent to exper­i­ment, also fea­tures. The impact factor for Nature Physics is 12.040, according to the ISI Journal Cita­tion Reports. This places Nature Physics first among all pri­mary research jour­nals in physics.

The journal fea­tures two pri­mary research paper for­mats: Let­ters and Arti­cles. In addi­tion to pub­lishing pri­mary research, Nature Physics serves as a cen­tral source for top-​​quality infor­ma­tion for the physics com­mu­nity through Review Arti­cles, News & Views, Research High­lights on impor­tant devel­op­ments pub­lished throughout the physics lit­er­a­ture, Com­men­taries, Book Reviews, and Correspondence.

About North­eastern:

Founded in 1898, North­eastern Uni­ver­sity is a pri­vate research uni­ver­sity located in the heart of Boston. North­eastern is a leader in inter­dis­ci­pli­nary research, urban engage­ment, and the inte­gra­tion of class­room learning with real-​​world expe­ri­ence. The university’s dis­tinc­tive coop­er­a­tive edu­ca­tion pro­gram, where stu­dents alter­nate semes­ters of full-​​time study with semes­ters of paid work in fields rel­e­vant to their pro­fes­sional inter­ests and major, is one of the largest and most inno­v­a­tive in the world. The Uni­ver­sity offers a com­pre­hen­sive range of under­grad­uate and grad­uate pro­grams leading to degrees through the doc­torate in six under­grad­uate col­leges, eight grad­uate schools, and two part-​​time divi­sions. For more infor­ma­tion, please visit www​.north​eastern​.edu.