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Title: Electromagnetic coupling of spins and pseudospins in bilayer graphene

Abstract

We present a detailed theoretical study of bilayer-graphene's electronic properties in the presence of electric and magnetic fields. Using group-theoretical methods, we derive an invariant expansion of the Hamiltonian for electron states near the K point of the Brillouin zone. In contrast to known materials, including single-layer graphene, any possible coupling of physical quantities to components of the external electric (magnetic) field has a counterpart where the analogous component of the magnetic (electric) field couples to exactly the same combination of quantities. For example, a purely electric spin splitting appears as the magnetoelectric analog of the familiar magnetic Zeeman spin splitting. The measurable thermodynamic response induced by magnetic and electric fields is thus completely symmetric. The Pauli magnetization induced by a magnetic field takes exactly the same functional form as the polarization induced by an electric field. Our findings thus reveal unconventional behavior of spin and pseudospin degrees of freedom in their coupling to external fields. We explain how these counterintuitive couplings are consistent with fundamental principles such as time reversal symmetry. For example, only a magnetic field can give rise to a macroscopic spin polarization, whereas only a perpendicular electric field can induce a macroscopic polarization of the sublattice-relatedmore » pseudospin degree of freedom characterizing the intravalley orbital motion in bilayer graphene. These rules enforced by symmetry for the matter-field interactions clarify the nature of spins versus pseudospins. We also provide numerical values of prefactors for relevant coupling terms. While our theoretical arguments use bilayer graphene as an example, they are generally valid for any material with similar symmetries. The unusual equivalence of magnetic and electric fields discussed here can provide the basis for designing more versatile device architectures for creating polarizations and manipulating the orientation of spins and pseudospins.« less

Authors:
;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science - Office of Basic Energy Sciences - Materials Sciences and Engineering Division; National Science Foundation (NSF)
OSTI Identifier:
1352825
DOE Contract Number:  
AC02-06CH11357
Resource Type:
Journal Article
Journal Name:
Physical Review. B, Condensed Matter and Materials Physics
Additional Journal Information:
Journal Volume: 91; Journal Issue: 20; Journal ID: ISSN 1098-0121
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English

Citation Formats

Winkler, R., and Zülicke, U. Electromagnetic coupling of spins and pseudospins in bilayer graphene. United States: N. p., 2015. Web. doi:10.1103/PhysRevB.91.205312.
Winkler, R., & Zülicke, U. Electromagnetic coupling of spins and pseudospins in bilayer graphene. United States. https://doi.org/10.1103/PhysRevB.91.205312
Winkler, R., and Zülicke, U. 2015. "Electromagnetic coupling of spins and pseudospins in bilayer graphene". United States. https://doi.org/10.1103/PhysRevB.91.205312.
@article{osti_1352825,
title = {Electromagnetic coupling of spins and pseudospins in bilayer graphene},
author = {Winkler, R. and Zülicke, U.},
abstractNote = {We present a detailed theoretical study of bilayer-graphene's electronic properties in the presence of electric and magnetic fields. Using group-theoretical methods, we derive an invariant expansion of the Hamiltonian for electron states near the K point of the Brillouin zone. In contrast to known materials, including single-layer graphene, any possible coupling of physical quantities to components of the external electric (magnetic) field has a counterpart where the analogous component of the magnetic (electric) field couples to exactly the same combination of quantities. For example, a purely electric spin splitting appears as the magnetoelectric analog of the familiar magnetic Zeeman spin splitting. The measurable thermodynamic response induced by magnetic and electric fields is thus completely symmetric. The Pauli magnetization induced by a magnetic field takes exactly the same functional form as the polarization induced by an electric field. Our findings thus reveal unconventional behavior of spin and pseudospin degrees of freedom in their coupling to external fields. We explain how these counterintuitive couplings are consistent with fundamental principles such as time reversal symmetry. For example, only a magnetic field can give rise to a macroscopic spin polarization, whereas only a perpendicular electric field can induce a macroscopic polarization of the sublattice-related pseudospin degree of freedom characterizing the intravalley orbital motion in bilayer graphene. These rules enforced by symmetry for the matter-field interactions clarify the nature of spins versus pseudospins. We also provide numerical values of prefactors for relevant coupling terms. While our theoretical arguments use bilayer graphene as an example, they are generally valid for any material with similar symmetries. The unusual equivalence of magnetic and electric fields discussed here can provide the basis for designing more versatile device architectures for creating polarizations and manipulating the orientation of spins and pseudospins.},
doi = {10.1103/PhysRevB.91.205312},
url = {https://www.osti.gov/biblio/1352825}, journal = {Physical Review. B, Condensed Matter and Materials Physics},
issn = {1098-0121},
number = 20,
volume = 91,
place = {United States},
year = {Fri May 01 00:00:00 EDT 2015},
month = {Fri May 01 00:00:00 EDT 2015}
}