arXiv subjects

Jakub Vonka

Publications and source records attributed to Jakub Vonka.

5 recordsLinked to original sources

arXiv2025

Strong electron-electron interactions in a dilute weakly-localized metal near a metal-to-insulator transition

Because it is easily switched from insulator to metal either via chemical doping or electrical gating, silicon is at the core of modern information technology and remains a candidate platform for quantum computing. The metal-to-insulator transition in this material has therefore been one of the most studied phenomena in condensed matter physics, and has been revisited with considerable profit each time a new fabrication technology has been introduced. Here we take advantage of recent advances in creating ultra-thin layers of Bohr-atom-like dopants to realize the two-dimensional disordered Hubbard model at half-filling and its metal-to-insulator transition (MIT) as a function of mean distance between atoms. We use gas-phase dosing of dopant precursor molecules on silicon to create arsenic and phosphorus $δ$-layers as thin as 0.4~nm and as dilute as 10$^{13}$~cm$^{-2}$. On approaching the insulating state, the conventional weak localization effects, prevalent at high dopant densities and due to orbital motion of the electrons in the plane, become dominated by electron-electron interaction contributions which obey a paramagnetic Zeeman scaling law. The latter make a negative contribution to the conductance, and thus cannot be interpreted in terms of an emergent Kondo regime near the MIT.

quant-ph↗

arXiv2025

Three-dimensional electronic domain correlations in 1T-TaS2

The interplay of nanoscale electronic domains underpins many emergent phenomena of quantum materials, including the competition between charge density waves (CDW) and superconductivity in high-Tc cuprates, or the storage of information in phase-change memory devices. Coupling to electronic domains provides an observable for pinpointing key interactions, e.g. affecting phase transitions. While the equilibrium phase diagram of 1T-TaS2 - characterized by unique transport properties and varying degrees of CDW commensurability - has been studied extensively, an understanding of how the electronic domains in the bulk behave across phase boundaries is lacking. We reveal the three-dimensional evolution of electronic domains in 1T-TaS2 using temperature-dependent X-ray diffraction and reciprocal space mapping, complemented by structure factor simulations based on the Hendricks-Teller method. With this methodology, we identify an increasing number of stacking faults near the phase transitions, and a growing fraction of dimerized layers in the commensurate phase upon cooling. We provide structural evidence that the CDW domains mediate the transport properties at phase boundaries, and that they also account for an anomalous intermediate electronic phase within the triclinic regime upon heating. As a paradigmatic material with potential in phase-change memory applications, our study underscores the importance of domain sizes and layer stacking in defining electronic behaviors of van der Waals materials.

cond-mat.str-el↗

arXiv2024

Absence of bulk charge density wave order in the normal state of UTe$_2$

A spatially modulated superconducting state, known as pair density wave (PDW), is a tantalizing state of matter with unique properties. Recent scanning tunneling microscopy (STM) studies revealed that spin-triplet superconductor UTe$_2$ hosts an unprecedented spin-triplet, multi-component PDW whose three wavevectors are indistinguishable from a preceding charge-density wave (CDW) order that survives to temperatures well above the superconducting critical temperature, $T_{c}$. Whether the PDW is the mother or a subordinate order remains unsettled. Here, based on a systematic search for bulk charge order above $T_{c}$ using resonant elastic X-ray scattering (REXS), we show that the structure factor of charge order previously identified by STM is absent in the bulk within the sensitivity of REXS. Our results invite two scenarios: either the density-wave orders condense simultaneously at $T_{c}$ in the bulk, in which case PDW order is likely the mother phase, or the charge modulations are restricted to the surface.

cond-mat.str-el↗

arXiv2021

Magnetotransport of dirty-limit van Hove singularity quasiparticles

Tuning of electronic density-of-states singularities is a common route to unconventional metal physics. Conceptually, van Hove singularities are realized only in clean two-dimensional systems. Little attention has therefore been given to the disordered (dirty) limit. Here, we provide a magnetotransport study of the dirty metamagnetic system calcium-doped strontium ruthenate. Fermi liquid properties persist across the metamagnetic transition, but with an unusually strong variation of the Kadowaki-Woods ratio. This is revealed by a strong decoupling of inelastic electron scattering and electronic mass inferred from density-of-state probes. We discuss this Fermi liquid behavior in terms of a magnetic field tunable van Hove singularity in the presence of disorder. More generally, we show how dimensionality and disorder control the fate of transport properties across metamagnetic transitions.

cond-mat.str-el↗

arXiv2016

Design and testing of low temperature part of an UHV SPM microscope

We have developed low temperature part of an ultra high vacuum scanning probe microscope (UHV-SPM) working at variable temperature within the range from 20 K to 700 K. To achieve the required temperature range, a flow cooling system using cryogenic helium (~5 K) as a coolant was designed. The system consists of a flow cryostat and a flexible low-loss transfer line connecting a Dewar vessel with the flow cryostat. We have also tested liquid nitrogen (~ 77 K) as an alternative low-cost coolant. Using nitrogen, the microscope can operate at temperatures of about 100 K and higher. As the flow of the coolant through the cryostat can cause thermally induced two-phase flow fluctuations resulting in instability in temperatures, preliminary tests were done in order to find ways of avoiding the temperature oscillations and optimising the cooling process.

physics.ins-det↗