arXiv subjects

Dominik Werhahn

Publications and source records attributed to Dominik Werhahn.

3 recordsLinked to original sources

arXiv2024

Effects of Chemical Pressure on Superconductivity in Electrochemically Intercalated (TMA)yFe2(Se1-xSx)2 (TMA = Tetramethylammonium)

The beta-modification of FeSe, which has an anti-PbO type structure, achieves superconductivity at 8 K without external doping or pressure and exhibits a nematic phase, which has been crucial for studies of unconventional pairing mechanisms. Although the critical temperature (Tc) in FeSe increases significantly with applied pressure, intercalation, and in thin films, the effect of replacing selenium with sulfur in FeSe1-xSx has remained unclear. To investigate the effects of chemical pressure, we have synthesized FeSe1-xSx crystals (up to x = 0.52) and intercalated them with tetramethylammonium ions (TMA+). Our results show that both Tc and unit cell volume decrease linearly with sulfur content in both host and intercalated (TMA)yFe2(Se1-xSx)2. The unexpected common rate of normalized decrease of Tc suggests that chemical pressure affects the electron-doped intercalates in the same way as the host compounds. This result highlights the unique role of chemical pressure and electron doping in tuning superconductivity in FeSe systems and provides new insights into their complex behavior.

cond-mat.supr-con↗

arXiv2023

Electronic nematicity without charge density waves in titanium-based kagome metal

Layered crystalline materials that consist of transition metal atoms on a kagome network have emerged as a versatile platform to study unusual electronic phenomena. For example, in the vanadium-based kagome superconductors AV3Sb5 (where A can stand for K, Cs, or Rb) there is a parent charge density wave phase that appears to simultaneously break both the translational and the rotational symmetry of the lattice. Here, we show a contrasting situation where electronic nematic order - the breaking of rotational symmetry without the breaking of translational symmetry - can occur without a corresponding charge density wave. We use spectroscopic-imaging scanning tunneling microscopy to study the kagome metal CsTi3Bi5 that is isostructural to AV3Sb5 but with a titanium atom kagome network. CsTi3Bi5 does not exhibit any detectable charge density wave state, but comparison to density functional theory calculations reveals substantial electronic correlation effects at low energies. Comparing the amplitudes of scattering wave vectors along different directions, we discover an electronic anisotropy that breaks the six-fold symmetry of the lattice, arising from both in-plane and out-of-plane titanium-derived d orbitals. Our work uncovers the role of electronic orbitals in CsTi3Bi5, suggestive of a hexagonal analogue of the nematic bond order in Fe-based superconductors.

cond-mat.str-el↗

arXiv2022

The kagomé metals RbTi$_3$Bi$_5$ and CsTi$_3$Bi$_5$

The kagomé metals RbTi$_3$Bi$_5$ and CsTi$_3$Bi$_5$ were synthesized both as polycrystalline powders by heating the elements an argon atmosphere and as single crystals grown using a self-flux method. The compounds crystallize in the hexagonal crystal system isotypically to KV$_3$Sb$_5$ (P6/mmm, Z = 1, CsTi3Bi5: a = 5.7873(1) Å, c = 9.2062(1) Å; RbTi3Bi5: a = 5.773(1) Å, c = 9.065(1) Å). Titanium atoms form a kagomé net with bismuth atoms in the hexagons as well as above and below the triangles. The alkali metal atoms are coordinated by 12 bismuth atoms and form AlB$_2$-like slabs between the kagomé layers. Magnetic susceptibility measurements with CsTi$_3$Bi$_5$ and RbTi$_3$Bi$_5$ single crystals reveal Pauli-paramagnetism and traces of superconductivity caused by CsBi$_2$/RbBi$_2$ impurities. Magnetotransport measurements reveal conventional Fermi liquid behavior and quantum oscillations indicative of a single dominant orbit at low temperature. DFT calculations show the characteristic metallic kagomé band structure similar to that of CsV$_3$Sb$_5$ with reduced band filling. A symmetry analysis of the band structure does not reveal an obvious and unique signature of a nontrivial topology.

cond-mat.mtrl-sci↗