Investigating quantum phase transitions using designer-anvil pressure cells

相关电子系统研究的发现发生在已知低温状态的边界上。仅次于外加磁场的是压力，它提供了对晶格密度的精确控制，是遍历量子物质相图和寻找物质新状态的首选工具。该项目代表了高压砧座技术的根本转变：我们将通过微刻技术将引线和检测电路结构到陶瓷砧座中。由此产生的设计锤提供了对原型关联电子超导体CeCu2Si2的高压超导状态进行新的研究所必需的可靠性、易用性和多功能性。在这一有趣的材料中，似乎有两种不同的机制可以在压力-温度相图的不同区域诱导超导电性。这两种相互作用都起源于电子之间的库仑排斥，但当材料在接近磁序开始时调谐时，其中一种-有效磁相互作用-占主导地位，而另一种-有效电荷密度相互作用-在假定的晶格相变附近占优势，在此过程中，单位晶胞体积和晶格密度经历了微弱的一级变化。为了研究CeCu2Si2及其相关材料的密度变化量子相变，我们将在100kbar范围内对其电阻率、热容和热膨胀的压力依赖性进行详细的研究。虽然所研究的配对机制可能会对包括高T_c超导体在内的强关联电子领域产生影响，但设想的高压技术将有利于大量对在顶锤条件下进行输运或热力学实验感兴趣的研究人员。

Discovery in correlated electron systems research occurs on the boundary of known low temperature states. Next to applied magnetic field, pressure, which affords precise control over the lattice density, is the vehicle of choice for traversing quantum matter phase diagrams and seeking out novel states of matter. This project represents a radical departure in high pressure anvil cell technology: We will structure leads and detection circuits into ceramic anvils by microlithographic methods. The resulting designer anvils provide the reliability, ease of use and versatility necessary for a novel investigation into the high-pressure superconducting state of the archetypal correlated electron superconductor CeCu2Si2. In this intriguing material it appears that two distinct mechanisms can induce superconductivity in different regions of the pressure-temperature phase diagram. Both interactions originate in the Coulomb repulsion between electrons, but one - an effective magnetic interaction - dominates when the material is tuned close to the onset of magnetic order, while the other - an effective charge density interaction - prevails close to a putative transition of the lattice, in which the unit cell volume and hence the lattice density undergoes a weak first order change. In order to investigate the density change quantum phase transition in CeCu2Si2 and in related materials, a detailed study of the pressure dependence of resistivity, heat capacity and thermal expansion will be carried out into the 100 kbar regime. While the investigated pairing mechanism may have ramifications throughout the strongly correlated electron field, including the high-Tc superconductors, the envisaged high pressure technology will be beneficial for a large community of researchers interested in transport or thermodynamic experiments under anvil cell conditions.