arXiv subjects

Anna Böhmer

Publications and source records attributed to Anna Böhmer.

3 recordsLinked to original sources

arXiv2016

Unconventional superconductors: Iron-based diversity

Nine years ago, superconductors based on the magnetic element iron were discovered. A flurry of research activity has revealed an unprecedented diversity of chemical structures and physical properties. Similarly to other unconventional superconductors, stripe-type antiferromagnetism seems to play an important role. Particularly interesting is its strong coupling to the crystal lattice. The systematic comparison of different compounds may allow to identify key elements in the mechanism of superconductivity and provide guidelines for the search for new and better superconductors.

cond-mat.supr-con↗

arXiv2015

Infrared study of the spin reorientation transition and its reversal in the superconducting state in underdoped Ba$ _{1-x} $K$ _{x} $Fe$ _{2} $As$ _{2} $

With infrared spectroscopy we investigated the spin-reorientation transition from an orthorhombic antiferromagnetic (o-AF) to a tetragonal AF (t-AF) phase and the reentrance of the o-AF phase in the superconducting state of underdoped Ba$ _{1-x} $K$ _{x} $Fe$ _{2} $As$ _{2} $. In agreement with the predicted transition from a single-$\mathbf{Q}$ to a double-$\mathbf{Q}$ AF structure, we found that a distinct spin density wave (SDW) develops in the t-AF phase. The pair breaking peak of this SDW acquires much more low-energy spectral weight than the one in the o-AF state which indicates that it competes more strongly with superconductivity. We also observed additional phonon modes in the t-AF phase which likely arise from a Brillouin-zone folding that is induced by the double-$\mathbf{Q}$ magnetic structure with two Fe sublattices exhibiting different magnitudes of the magnetic moment.

cond-mat.supr-con↗

arXiv2011

Thermal expansion and Grüneisen parameters of Ba(Fe1-xCox)2As2 - a thermodynamic quest for quantum criticality

Thermal expansion data are used to study the uniaxial pressure dependence of the electronic/magnetic entropy of Ba(Fe1-xCox)2As2. Uniaxial pressure is found to be proportional to doping and, thus, also an appropriate tuning parameter in this system. Many of the features predicted to occur for a pressure-tuned quantum critical system, in which superconductivity is an emergent phase hiding the critical point, are observed. The electronic/magnetic Grüneisen parameters associated with the spin-density wave and superconducting transitions further demonstrate an intimate connection between both ordering phenomena.

cond-mat.supr-con↗