$_x$ TiSe $_2$ Cu单晶的磁性和热力学性质
Magnetic and thermodynamic properties of Cu$_x$TiSe$_2$ single crystals
摘要：
我们提出了一个详细的研究的相图铜插层TiSe $_2$单晶，结合本地霍尔探针磁强计，隧道二极管振荡器技术（TDO），比热，角分辨光电子能谱测量。本文研究了三种不同来源的具有不同铜含量$x$和超导临界温度$T_c$的一系列Cu $_x$ TiSe $_2$样品。我们首先表明，涡流穿透机制是占主导地位的几何障碍，使一个精确的测定较低的临界场，$H_{c1}$。然后，我们表明，从磁测量（$H_{c1}$和TDO技术）推导出的超流密度的温度依赖性清楚地表明存在一个小的能隙在系统中，与耦合强度$2Δ_s \sim [2.4-2.8]k_BT_c$，无论铜含量，在令人费解的矛盾与比热测量，可以很好地描述了一个单一的大间隙$2Δ_l \sim [3.7-3.9]k_BT_c$。最后，我们的测量揭示了一个非平凡的掺杂依赖的凝聚能，这仍然有待理解。
英文摘要：
We present a detailed study of the phase diagram of copper intercalated TiSe$_2$ single crystals, combining local Hall-probe magnetometry, tunnel diode oscillator technique (TDO), specific-heat, and angle-resolved photoemission spectroscopy measurements. A series of the Cu$_x$TiSe$_2$ samples from three different sources with various copper content $x$ and superconducting critical temperatures $T_c$ have been investigated. We first show that the vortex penetration mechanism is dominated by geometrical barriers enabling a precise determination of the lower critical field, $H_{c1}$. We then show that the temperature dependence of the superfluid density deduced from magnetic measurements (both $H_{c1}$ and TDO techniques) clearly suggests the existence of a small energy gap in the system, with a coupling strength $2Δ_s \sim [2.4-2.8]k_BT_c$, regardless of the copper content, in puzzling contradiction with specific heat measurements which can be well described by one single large gap $2Δ_l \sim [3.7-3.9]k_BT_c$. Finally, our measurements reveal a non-trivial doping dependence of the condensation energy, which remains to be understood.
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