arXiv subjects

Erik Kampert

Publications and source records attributed to Erik Kampert.

6 recordsLinked to original sources

arXiv2023

Absence of Fermi surface reconstruction in pressure-driven overdoped YBCO

The evolution of the critical superconducting temperature and field, quantum oscillation frequencies and effective mass $m^{*}$ in underdoped YBa$_2$Cu$_3$O$_{7-δ}$ (YBCO) crystals ($p$ = 0.11, with $p$ the hole concentration per Cu atom) points to a partial suppression of the charge orders with increasing pressure up to 7 GPa, mimicking doping. Application of pressures up to 25 GPa pushes the sample to the overdoped side of the superconducting dome. Contrary to other cuprates, or to doping studies on YBCO, the frequency of the quantum oscillations measured in that pressure range do not support the picture of a Fermi-surface reconstruction in the overdoped regime, but possibly point to the existence of a new charge order.

cond-mat.supr-con↗

arXiv2020

Anomalous Hall effect in Weyl semimetal half Heusler compounds RPtBi (R = Gd and Nd)

Topological materials ranging from topological insulators to Weyl and Dirac semimetals form one of the most exciting current fields in condensed-matter research. Many half-Heusler compounds, RPtBi (R= rare earth) have been theoretically predicted to be topological semimetals. Among various topological attributes envisaged in RPtBi, topological surface states, chiral anomaly and planar Hall effect have been observed experimentally. Here, we report on an unusual intrinsic anomalous Hall effect (AHE) in the antiferromagnetic Heusler Weyl semimetal compounds GdPtBi and NdPtBi that is observed over a wide temperature range. In particular, GdPtBi exhibits an anomalous Hall conductivity of up to 60 ohm-1cm-1 and an anomalous Hall angle as large as 23%. Muon spin resonance (mu-SR) studies of GdPtBi indicate a sharp antiferromagnetic transition (T_N) at 9 K without any noticeable magnetic correlations above T_N. Our studies indicate that Weyl points in these half-Heuslers are induced by a magnetic field via exchange-splitting of the electronic bands at or near to the Fermi energy which is the source of the chiral anomaly and the AHE.

cond-mat.mtrl-sci↗

arXiv2018

Magnetocrystalline anisotropy and exchange probed by high-field anomalous Hall effect in fully-compensated half-metallic Mn2RuxGa thin films

Magnetotransport is investigated in thin films of the half-metallic ferrimagnet Mn$_2$Ru$_x$Ga in pulsed magnetic fields of up to 58 T. A non-vanishing Hall signal is observed over a broad temperature range, spanning the compensation temperature 155 K, where the net magnetic moment is strictly zero, the anomalous Hall conductivity is 6673 $Ω^{-1}.m^{-1}$ and the coercivity exceeds 9 T. Molecular field modelling is used to determine the intra- and inter-sublattice exchange constants and from the spin-flop transition we infer the anisotropy of the electrically active sublattice to be 216 kJ/m$^3$ and predict the magnetic resonances frequencies. Exchange and anisotropy are comparable and hard-axis applied magnetic fields result in a tilting of the magnetic moments from their collinear ground state. Our analysis is applicable to collinear ferrimagnetic half-metal systems.

cond-mat.mtrl-sci↗

arXiv2018

Fractional Quantum Hall plateaus in mosaic-like conductors

We report a simple route to generate magnetotransport data that results in fractional quantum Hall plateaus in the conductance. Ingredients to the generating model are conducting tiles with integer quantum Hall effect and metallic linkers, further Kirchhoff rules. When connecting few identical tiles in a mosaic, fractional steps occur in the conductance values. Richer spectra representing several fractions occur when the tiles are parametrically varied. Parts of the simulation data are supported with purposefully designed graphene mosaics in high magnetic fields. The findings emphasize that the occurrence of fractional conductance values, in particular in two-terminal measurements, does not necessarily indicate interaction-driven physics. We underscore the importance of an independent determination of charge densities and critically discuss similarities with and differences to the fractional quantum Hall effect.

cond-mat.mes-hall↗

arXiv2015

Large linear magnetoresistance and weak anti-localization in Y(Lu)PtBi topological insulators

Topological insulators are new kind of Dirac materials that possess bulk insulating and surface conducting behavior. They are basically known for their unique electronic properties at the surface. Here we present the magneto-transport properties of our high quality single crystalline Y(Lu)PtBi Heusler topological insulators, which belong to a group of noncentrosymmetric superconductor with Tc = 0:8 K. Both the compounds show semi-metallic behavior with low charge carrier of 6 x1018 cm^-3 for YPtBi and 8 x1019 cm^-3 for LuPtBi at 2 K. Magneto-conductivity measurements in the tilted field indicate that the charge carriers transport through quantum interference. This provide a direct evidence of weak anti-localization below 50 K, giving a strong signature of surface transport. Most importantly, these compounds show very high unsaturated linear magnetoresistance of approximately 2000% at 10 K in a magnetic field of 60 T.

cond-mat.mtrl-sci↗

arXiv2014

Nonmetallic Low-Temperature Normal State of K0.70Fe1.46Se1.85Te0.15

The normal-state in-plane resistivity below the zero-field superconducting transition temperature $T_c$ and the upper critical field Hc2 were measured by suppressing superconductivity in pulsed magnetic fields for K0.70Fe1.46Se1.85Te0.15. The normal-state resistivity $ρ_{ab}$ is found to increase logarithmically with decrasing temperature as $\frac{T}{T_c}\rightarrow 0$. Similar to granular metals, our results suggest that a superconductor - insulator transition below zero-field T$_{c}$ may be induced in high magnetic fields. This is related to the intrinsic real-space phase-separated states common to all inhomogeneous superconductors.

cond-mat.supr-con↗