Experimental signatures of the mixed axial-gravitational anomaly in the Weyl semimetal NbP

被引:222
|
作者
Gooth, Johannes [1 ,2 ]
Niemann, Anna C. [1 ,3 ]
Meng, Tobias [4 ]
Grushin, Adolfo G. [5 ]
Landsteiner, Karl [6 ]
Gotsmann, Bernd [2 ]
Menges, Fabian [2 ]
Schmidt, Marcus [7 ]
Shekhar, Chandra [7 ]
Suess, Vicky [7 ]
Huehne, Ruben [3 ]
Rellinghaus, Bernd [3 ]
Felser, Claudia [7 ]
Yan, Binghai [7 ,8 ]
Nielsch, Kornelius [1 ,3 ]
机构
[1] Univ Hamburg, Inst Nanostruct & Solid State Phys, Jungiusstr 11, D-20355 Hamburg, Germany
[2] IBM Res Zurich, Saumerstr 4, CH-8803 Ruschlikon, Switzerland
[3] Leibniz Inst Solid State & Mat Res Dresden, Inst Metall Mat, Helmholtzstr 20, D-01069 Dresden, Germany
[4] Tech Univ Dresden, Inst Theoret Phys, Zellescher Weg 17, D-01062 Dresden, Germany
[5] Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720 USA
[6] Univ Autonoma Madrid, CSIC, Inst Fis Teor, Nicolas Cabrera 13-15, Madrid 28049, Spain
[7] Max Planck Inst Chem Phys Solids, Nothnitzer Str 40, D-01187 Dresden, Germany
[8] Weizmann Inst Sci, Dept Condensed Matter Phys, IL-7610001 Rehovot, Israel
关键词
NEGATIVE MAGNETORESISTANCE; FERMION SEMIMETAL; THERMOPOWER; DISCOVERY; ARCS;
D O I
10.1038/nature23005
中图分类号
O [数理科学和化学]; P [天文学、地球科学]; Q [生物科学]; N [自然科学总论];
学科分类号
07 ; 0710 ; 09 ;
摘要
The conservation laws, such as those of charge, energy and momentum, have a central role in physics. In some special cases, classical conservation laws are broken at the quantum level by quantum fluctuations, in which case the theory is said to have quantum anomalies(1). One of the most prominent examples is the chiral anomaly(2,3), which involves massless chiral fermions. These particles have their spin, or internal angular momentum, aligned either parallel or antiparallel with their linear momentum, labelled as left and right chirality, respectively. In three spatial dimensions, the chiral anomaly is the breakdown (as a result of externally applied parallel electric and magnetic fields(4)) of the classical conservation law that dictates that the number of massless fermions of each chirality are separately conserved. The current that measures the difference between left- and right-handed particles is called the axial current and is not conserved at the quantum level. In addition, an underlying curved space-time provides a distinct contribution to a chiral imbalance, an effect known as the mixed axial-gravitational anomaly(1), but this anomaly has yet to be confirmed experimentally. However, the presence of a mixed gauge-gravitational anomaly has recently been tied to thermoelectrical transport in a magnetic field(5,6), even in flat space-time, suggesting that such types of mixed anomaly could be experimentally probed in condensed matter systems known as Weyl semimetals(7). Here, using a temperature gradient, we observe experimentally a positive magneto-thermoelectric conductance in the Weyl semimetal niobium phosphide (NbP) for collinear temperature gradients and magnetic fields that vanishes in the ultra-quantum limit, when only a single Landau level is occupied. This observation is consistent with the presence of a mixed axial-gravitational anomaly, providing clear evidence for a theoretical concept that has so far eluded experimental detection.
引用
收藏
页码:324 / +
页数:18
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