arXiv subjects

Jooseop Lee

Publications and source records attributed to Jooseop Lee.

4 recordsLinked to original sources

arXiv2025

Large Kohn anomaly and phonon collapse induced by charge density wave in UPt$_2$Si$_2$

Using high-energy-resolution inelastic x-ray scattering, we observe anomalous softening and damping of the transverse acoustic phonon in UPt$_2$Si$_2$ as the system is cooled towards the charge density wave (CDW) transition temperature, T$_{\rm{CDW}}$. The phonon exhibits a marked Kohn-type anomaly around the CDW wave vector, Q$_{\rm{CDW}}$, and becomes overdamped within a finite momentum range already well above T$_{\rm{CDW}}$. The dispersion anomaly is consistent with potential Fermi surface nesting, which together with the extended phonon collapse indicate strong electron-phonon coupling. The transition temperature estimated from the phonon softening is markedly lower than T$_{\rm{CDW}}$, consistent with a primarily electronic instability rather than a phonon-driven transition. Our results establish UPt$_2$Si$_2$ as a prime example of a strongly correlated electron CDW system with exceptionally strong electron-phonon coupling driving phonon softening and collapse.

cond-mat.str-el↗

arXiv2021

Direct Observation of an Incommensurate Charge Density Wave in the BiS2-based Superconductor NdO1-xFxBiS2

The nature of superconductivity in BiS$_2$-based superconductors has been controversial while ab-initio calculations proposed this system in close proximity to a charge-density-wave (CDW) phase. Using high-energy high-flux X-ray diffraction, we reveal an intrinsic and long-range CDW phase coexisting with superconductivity in NdO$_{1-x}$F$_{x}$BiS$_2$ superconductor ($x$ = 0.37 and 0.3). The CDW wavevector in NdO$_{0.63}$F$_{0.37}$BiS$_2$ correspond Q$_{\rm{CDW}}$ = (0.17, 0.17, 0.5) and is associated with transverse atomic displacements. Interestingly, this wavevector does not match theoretical expectations based on either phonon softening or Fermi surface nesting. In NdO$_{0.7}$F$_{0.3}$BiS$_2$, where the superconducting transition temperature is highest, the CDW satellites are slightly broader and weaker compared to NdO$_{0.63}$F$_{0.37}$BiS$_2$, possibly suggesting the competition with the superconductivity. Lastly, we measure a thermal diffuse scattering across the superconducting transition temperature and find no meaningful changes in favor of the unconventional pairing mechanism. Our result suggests the importance of understanding CDW which might hold a key to the superconductivity in the BiS$_2$-based superconductor.

cond-mat.supr-con↗

arXiv2020

Charge density wave with anomalous temperature dependence in UPt2Si2

Using single crystal neutron and x-ray diffraction, we discovered a charge density wave (CDW) below 320 K, which accounts for the long-sought origin of the heat capacity and resistivity anomalies in UPt2Si2. The modulation wavevector, Qmod, is intriguingly similar to the Fermi surface nesting wavevector of URu2Si2. Qmod shows an unusual temperature dependence, shifting from commensurate to incommensurate position upon cooling and becoming locked at ~ (0.42 0 0) near 180 K. Bulk measurements indicate a cross-over toward a correlated coherent state around the same temperature, suggesting an interplay between the CDW and Kondo-lattice-like coherence before coexisting antiferromagnetic order sets in at TN = 35 K.

cond-mat.supr-con↗

arXiv2018

The dual nature of magnetism in a uranium heavy fermion system

The duality between localized and itinerant nature of magnetism in $5\textit{f}$ electron systems has been a longstanding puzzle. Here, we report inelastic neutron scattering measurements, which reveal both local and itinerant aspects of magnetism in a single crystalline system of UPt$_{2}$Si$_{2}$. In the antiferromagnetic state, we observe broad continuum of diffuse magnetic scattering with a resonance-like gap of $\approx$ 7 meV, and surprising absence of coherent spin-waves, suggestive of itinerant magnetism. While the gap closes above the Neel temperature, strong dynamic spin correlations persist to high temperature. Nevertheless, the size and temperature dependence of the total magnetic spectral weight can be well described by local moment with $J=4$. Furthermore, polarized neutron measurements reveal that the magnetic fluctuations are mostly transverse, with little or none of the longitudinal component expected for itinerant moments. These results suggest that a dual description of local and itinerant magnetism is required to understand UPt$_{2}$Si$_{2}$, and by extension, other 5$f$ systems in general.

cond-mat.supr-con↗