[Zurück]

Sami Dzsaber, L. Prochaska, A. Sidorenko, Gaku Eguchi, R. Svagera, M. Waas, A. Prokofiev, Q. Si, S. Paschen:
"Kondo insulator to semimetal transformation tuned by spin-orbit coupling";
Vortrag: SCTE2018, The 21st International Conference on Solid Compounds of Transition Elements, Wien; 25.03.2018 - 29.03.2018.

The recent discovery of topologically non-trivial bandstructures in weakly interacting electron systems [1] has
triggered enormous efforts in the search for their strongly correlated counterparts. An ideal setting in this quest are
heavy fermion systems. In these materials, the localized 4f electrons - characterized by a strong Coulomb repulsion
- couple to the conduction band via the Kondo effect, to either form a Fermi sea of heavy quasi-particles (heavy
fermion (semi)metals), or to open a correlation gap in an otherwise metallic system (Kondo insulators).
Untill recently, topological Kondo insulator (most notably SmB6) were at the forefront of the field. Therein, the
strong spin-orbit coupling of the 4f electrons of the rare earth elements are considered to play the key role [2],
where as the spin-orbit interaction among the conduction electrons (lSO) has received comparably little attention.
However, very recently, gapless versions forming Dirac-Kondo- and Weyl-Kondo semimetals have attracted much
attention [3,4]. Therein, it is theoretically predicted that lSO determines the topology, and is expected to tune
between different phases [3]. In these systems, the topologically protected bands correspond to the bulk of the
system, allowing for bulk sensitive measuremnts, where the strong electron interaction can be most robustly
tracked.
In the present work, we introduce for the first time lSO as a systematic experimental tuning parameter in a Kondo
insulator [5]. Starting form the archetypal cubic non-centrosymmetric Kondo insulator Ce3Bi4Pt3 [6,7], we have
grown a series of Ce3Bi4(Pt1-xPdx)3 single crystals [5]. The substitution series is iso-structural, iso-electronic, and
iso-size, leaving lSO as the main tuning parameter, while the otherwise dominant chemical potential and Kondo
coupling variations are kept minimal. Upon gradually replacing the heavy 5d element Pt by the much lighter 4d
element Pd, we observe an insulator-to-semimetal transitiont, that we attribute to the decreasing of lSO. Most
interestingly, the low-temperature electronic specific heat coefficient Cel/T of Ce3Bi4Pd3 is linear in T 2 , with a slope
that is sizably larger than any phonon contribution. This is the hallmark of a strongly correlated system with linear
electronic dispersion, as the recently predicted Weyl-Kondo semimetal [4].
We gratefully acknowledge financial support from the Austrian Science Fund (doctoral program W1243 and I2535-
N27) and the U.S. Army Research Office (ARO Grant No.W911NF-14-1-0496) in Vienna, and the ARO (Grant
No.W911NF-14-1-0525) and the Robert A. Welch Foundation (Grant No. C-1411) at Rice.
[1] A. Bansil, H. Lin, and T. Das, Rev. Mod. Phys. 88, 021004 (2016).
[2] M. Dzero, J. Xia, V. Galitski and P. Coleman, Rev. Condens. Matter. Phys, 7, 249 (2016).
[3] X.-Y. Feng, J. Dai, C.-H. Chung, and Q. Si, Phys. Rev. Lett., 111, 016402 (2013).
[4] H.-H. Lai, S. E. Grefe, S. Paschen, and Q. Si, PNAS, in press (2017)
[5] S. Dzsaber, L. Prochaska, A. Sidorenko, G. Eguchi, R. Svagera, M. Waas, A. Prokofiev, Q. Si, and S. Paschen,
Phys. Rev. Lett., 118, 246601 (2017).
[6] M.F. Hundley, P. C. Canfield, J. D. Thompson, Z. Fisk, and J. M. Lawrence Phys. Rev. B 42, 6842 (1990).
[7] M. Jaime, R. Movshovich, G. Stewart, W. Beyermann, M. Berisso, M. Hundley, P. Canfield, and J. Sarrao,
Nature, 45, 160 (2000).
[7] H.-H. Lai, S. E. Grefe, S. Paschen, and Q. Si, PNAS, in press (2017)

Topology, Weyl, Kondo, Spin-orbit coupling