We present electrical resistivity and ac-susceptibility measurements of GdTe$_3$, TbTe$_3$ and DyTe$_3$ performed under pressure. An upper charge-density-wave (CDW) is suppressed at a rate of $mathrm{d}T_{mathrm{CDW,1}}/mathrm{d}P$ = $-$85 K/GPa. For
TbTe$_3$ and DyTe$_3$, a second CDW below $T_{mathrm{CDW,2}}$ increases with pressure until it reaches the $T_{mathrm{CDW,1}}$($P$) line. For GdTe$_3$, the lower CDW emerges as pressure is increased above $sim$ 1 GPa. As these two CDW states are suppressed with pressure, superconductivity (SC) appears in the three compounds at lower temperatures. Ac-susceptibility experiments performed on TbTe$_3$ provide compelling evidence for bulk SC in the low-pressure region of the phase diagram. We provide measurements of superconducting critical fields and discuss the origin of a high-pressure superconducting phase occurring above 5 GPa.
We present a study of the Fermi surface of KFe$_2$As$_2$ single crystals. Quantum oscillations were observed in magnetostriction measured down to 50 mK and in magnetic fields $H$ up to 14 T. For $H parallel c$, the calculated effective masses are in
agreement with recent de Haas-van Alphen and ARPES experiments, showing enhanced values with respect to the ones obtained from previous band calculations. For $H parallel a$, we observed a small orbit at a cyclotron frequency of 64 T, characterized by an effective mass of $sim 0.8 m_e$, supporting the presence of a three-dimensional pocket at the Z-point.
The upper critical field Hc2(T) of the multiband superconductor KFe2As2 has been studied via low-temperature thermal expansion and magnetostriction measurements. We present compelling evidence for Pauli-limiting effects dominating Hc2(T) for H || a,
as revealed by a crossover from second- to first-order phase transitions to the superconducting state in the magnetostriction measurements down to 50 mK. Corresponding features were absent for H || c. To our knowledge, this crossover constitutes the first confirmation of Pauli limiting of the Hc2(T) of a multiband superconductor. The results are supported by modeling Pauli limits for single-band and multiband cases.
The low-temperature thermal expansion of CeCoIn5 single crystals measured parallel and perpendicular to magnetic fields B oriented along the c axis yields the volume thermal-expansion coefficient $beta$. Considerable deviations of $beta(T)$ from Ferm
i-liquid behavior occur already within the superconducting region of the (B, T) phase diagram and become maximal at the upper critical field $B^0_{c2}$. However, $beta(T)$ and the Gruneisen parameter $Gamma$ are incompatible with a quantum critical point (QCP) at $B^0_{c2}$, but allow for a QCP shielded by superconductivity and extending to negative pressures for $B < B^0_{c2}$. Together with literature data we construct a tentative (p, B, T) phase diagram of CeCoIn5 suggesting a quantum critical line in the (p, B) plane.
