Second-Harmonic Response in Magnetic Nodal-Line Semimetal Fe₃GeTe₂

Abstract

We experimentally investigate second-harmonic transverse voltage response to ac electrical current for a magnetic nodal-line semimetal Fe$_3$GeTe$_2$. For zero magnetic field, the observed second-harmonic voltage depends as a square of the longitudinal current, as it should be expected for non-linear Hall effect. The magnetic field behavior is found to be sophisticated:while the first-harmonic response shows the known anomalous Hall hysteresis in FGT, the second-harmonic Hall voltage is characterized by the pronounced high-field hysteresis and flat ($B$-independent) region with curves touching at low fields. The high-field hysteresis strongly depends on the magnetic field sweep rate, so it reflects some slow relaxation process. For the lowest rates, it is also accomplished by multiple crossing points. Similar shape of the second-harmonic hysteresis is known for skyrmion spin textures in non-linear optics. Since skyrmions have been demonstrated for FGT by direct visualization techniques, we can connect the observed high-field relaxation with deformation of the skyrmion lattice. Thus, the second-harmonic Hall voltage response can be regarded as a tool to detect spin textures in transport experiments.

Gate-Dependent Nonlinear Hall Effect at Room Temperature in Topological Semimetal GeTe

“…sponse is much easier to be measured by standard lock-in technique. [18][19][20][21][22][23] On the other hand, zero-frequency NLH response can be used for high-frequency (even terahertz or infrared) detection, [24,25] which is important for wide-band communications, [26] wireless charging, energy harvesting, etc. An advantage of the NLH rectification is the absence of thermal losses, since it originates from the Berry curvature dipole.…”

“…[37][38][39][40][41][42][43][44] We investigate transverse (𝑥𝑦-) first-and secondharmonic voltage responses by standard four-point lock-in technique. [20,22,23] The ac current is applied between C1 and C3 contacts in Fig. 1(b), while the transverse (Hall) voltage 𝑈𝑥𝑦 is measured between the C2 and C6 potential probes.…”

Gate-Tunable Lifshitz Transition of Fermi Arcs and Its Transport Signatures

“…According to features of band degeneracies, topological semimetals can be further classified into several types, including Weyl semimetals (WSMs), Dirac semimetals, [4][5][6] and nodal-line semimetals. [10][11][12] As counterparts of massless Weyl and Dirac fermions in condensed matter physics, quasiparticles with linear dispersion in WSMs and Dirac semimetals provide an interesting platform for exploring novel effects predicted by high-energy physics. [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] These effects are manifested as anomalous transport and optical properties which can be probed using a standard approach of condensed matter physics.…”