Pressure Induced Superconductivity in Pristine 1T-TiSe2

The interplay between superconductivity and the charge-density wave (CDW) state in pure 1T-TiSe2 is examined through a high-pressure study extending up to pressures of 10 GPa between sub-Kelvin and room temperatures. At a critical pressure of 2 GPa a superconducting phase sets in and persists up to pressures of 4 GPa. The maximum superconducting transition temperature is 1.8 K. These findings complement the recent discovery of superconductivity in copper-intercalated 1T-TiSe2. The comparisons of the normal state and superconducting properties of the two systems reveal the possibility that the emergent electronic state qualitatively depends on the manner in which the CDW state is destabilized, making this a unique example where two different superconducting domes are obtained by two different methods from the same parent compound.

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Helmuth Berger, László Forró, Balazs Sipos, Eduard Tutis
2009
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https://infoscience.epfl.ch/record/159115?ln=en

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Superconductivity

Superconductivity is a set of physical properties observed in certain materials where electrical resistance vanishes and magnetic fields are expelled from the material. Any material exhibiting these

Charge density wave

A charge density wave (CDW) is an ordered quantum fluid of electrons in a linear chain compound or layered crystal. The electrons within a CDW form a standing wave pattern and sometimes collectively

High-temperature superconductivity

High-temperature superconductors (abbreviated high-Tc or HTS) are defined as materials with critical temperature (the temperature below which the material behaves as a superconductor) a

From Mott state to superconductivity in 1T-TaS2

Ana Akrap, Helmuth Berger, László Forró, Balazs Sipos, Eduard Tutis

The search for the coexistence between superconductivity and other collective electronic states in many instances promoted the discovery of novel states of matter. The manner in which the different types of electronic order combine remains an ongoing puzzle. 1T-TaS2 is a layered material, and the only transition-metal dichalcogenide (TMD) known to develop the Mott phase. Here, we show the appearance of a series of low-temperature electronic states in 1T-TaS2 with pressure: the Mott phase melts into a textured charge-density wave (CDW); superconductivity develops within the CDW state, and survives to very high pressures, insensitive to subsequent disappearance of the CDW state and, surprisingly, also the strong changes in the normal state. This is also the first reported case of superconductivity in a pristine 1T-TMD compound. We demonstrate that superconductivity first develops within the state marked by a commensurability-driven, Coulombically frustrated, electronic phase separation.

2008

Inhomogeneity of charge-density-wave order and quenched disorder in a high-T-c superconductor

Davide Innocenti, Janusz Andrzej Karpinski

It has recently been established that the high-transition-temperature (high-T-c) superconducting state coexists with short-range charge-density-wave order(1-11) and quenched disorder(12,13) arising from dopants and strain(14-17). This complex, multiscale phase separation(18-21) invites the development of theories of high-temperature superconductivity that include complexity(22-25). The nature of the spatial interplay between charge and dopant order that provides a basis for nanoscale phase separation remains a key open question, because experiments have yet to probe the unknown spatial distribution at both the nanoscale and mesoscale (between atomic and macroscopic scale). Here we report micro X-ray diffraction imaging of the spatial distribution of both short-range charge-density-wave 'puddles' (domains with only a few wavelengths) and quenched disorder in HgBa2CuO4+y, the single-layer cuprate with the highest T-c, 95 kelvin (refs 26-28). We found that the charge-density-wave puddles, like the steam bubbles in boiling water, have a fat-tailed size distribution that is typical of self-organization near a critical point(19). However, the quenched disorder, which arises from oxygen interstitials, has a distribution that is contrary to the usually assumed random, uncorrelated distribution(12,13). The interstitial-oxygen-rich domains are spatially anticorrelated with the charge-density-wave domains, because higher doping does not favour the stripy charge-density-wave puddles, leading to a complex emergent geometry of the spatial landscape for superconductivity.

Nature Publishing Group2015

Superconductor–insulator transition in La2 − xSrxCuO4 at the pair quantum resistance

Ivan Bozovic, Guy Joseph Günter Dubuis, Davor Pavuna

High-temperature superconductivity in copper oxides arises when a parent insulator compound is doped beyond some critical concentration; what exactly happens at this superconductor–insulator transition is a key open question1. The cleanest approach is to tune the carrier density using the electric field effect2, 3, 4, 5, 6, 7; for example, it was learned in this way5 that weak electron localization transforms superconducting SrTiO3 into a Fermi-glass insulator. But in the copper oxides this has been a long-standing technical challenge3, because perfect ultrathin films and huge local fields (>109 V m−1) are needed. Recently, such fields have been obtained using electrolytes or ionic liquids in the electric double-layer transistor configuration8, 9, 10. Here we report synthesis of epitaxial films of La2− xSrxCuO4 that are one unit cell thick, and fabrication of double-layer transistors. Very large fields and induced changes in surface carrier density enable shifts in the critical temperature by up to 30 K. Hundreds of resistance versus temperature and carrier density curves were recorded and shown to collapse onto a single function, as predicted for a two-dimensional superconductor–insulator transition11, 12, 13, 14. The observed critical resistance is precisely the quantum resistance for pairs, RQ = h/(2e)2 = 6.45 kΩ, suggestive of a phase transition driven by quantum phase fluctuations, and Cooper pair (de)localization.

2011