- 03 Oct 2022
- 14h00 - 18h00
Arthur Veyrat I Low dimensionality and Weyl topology in layered trigonal-PtBi2
Institute for Solid State Research, Leibniz Institute for Solid State and Materials Research,
In the last few years Weyl semimetals have attracted considerable attention as they are predicted
to display new and exotic physics, for instance a new type of topological superconductivity.
In this seminar, I will present a low temperature charge transport study of the newly predicted
Weyl semimetal trigonal-PtBi2, focusing on two main results: the discoveries of superconductivity
and planar Hall Effect in thin exfoliated flakes of t-PtBi2.
While superconductivity has already been found under pressure in t-PtBi2 above 2K (1, 2),
we found that single crystals of t-PtBi2 also display superconductivity at ambient pressure, with a
critical temperature Tc ∼ 600mK (3). When thinning down the crystals using mechanical exfolia-
tion, the superconductivity changes with the thickness, with a reduction of the critical temperature
down to Tc ∼ 350mK. The superconductivity also becomes two-dimensional when reducing the
thickness below arround t ∼ 60nm. Remarkably, even at such large thicknesses nanostructures
show clear evidence of Berezinskii–Kosterlitz–Thouless (BKT) transitions, demonstrating the low
dimensionality of the superconductivity.
At higher temperature (in the normal state), we found that the in-plane magnetoresistance is
highly dependent on the angle between the in-plane magnetic field and the current flowing in the
sample, with a π-periodic dependence of both the longitudinal and transverse magnetoresistances
when rotating the field in the sample’s plane, and a π/4 phase offset between the two. This is
typical of the so called planar Hall effect (PHE), which can be a signature of Weyl topology in
non-magnetic materials (4, 5), and has been found to be a more accurate effect to experimentally
unveil Weyl physics in samples than the chiral anomaly, which can be hidden in materials with a
large orbital magnetoresistance (6).
An additional 2π-periodic angular dependence is found in the transverse resistance, which might
be a manifestation on a recently predicted anomalous planar Hall effect (APHE) (7 ), and should
appear as a result of a non-vanishing Berry curvature in materials with broken C2 symmetry.
1. J. Wang et al., Physical Review B 103, Publisher: American Physical Society, 1–6, ISSN:
2. D. L. Bashlakov et al., arXiv e-prints, arXiv: 2205.06610, (https://arxiv.org/abs/2205.
06610v1) (May 2022).
3. A. Veyrat et al., arXiv e-prints, arXiv: 2101.01620, (http://arxiv.org/abs/2101.01620)
4. A. A. Burkov, Physical Review B 96, 041110, ISSN: 2469-9950, (http://link.aps.org/doi/
10.1103/PhysRevB.96.041110) (July 2017).
5. S. Nandy, G. Sharma, A. Taraphder, S. Tewari, Physical Review Letters 119, 1–6, ISSN:
6. P. Li et al., Physical Review B 100, Publisher: American Physical Society, 205128, ISSN:
2469-9950, (https://link.aps.org/doi/10.1103/PhysRevB.100.205128) (Nov. 2019).
7. R. Battilomo, N. Scopigno, C. Ortix, Physical Review Research 3, Publisher: American Phys-
ical Society, 1–6, ISSN: 2643-1564 (2021).