APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016;
Baltimore, Maryland
Session V1: Non-Equilibrium Aspects of Electron-Boson Coupling in High Temperature Superconductors
2:30 PM–5:30 PM,
Thursday, March 17, 2016
Room: Ballroom I
Sponsoring
Units:
DCMP DMP
Chair: Zhi-Xun Shen, Stanford University
Abstract ID: BAPS.2016.MAR.V1.5
Abstract: V1.00005 : Optical probes of symmetry breaking in magnetic and superconducting BaFe$_{2}$(As$_{1-x}$P$_{x})_{2}$*
4:54 PM–5:30 PM
Preview Abstract
Abstract
Author:
Joseph Orenstein
(UC Berkeley/LBNL)
The discovery of iron pnictide superconductors has opened promising new
directions in the effort to fully understand the phenomenon of
high-$T_{c}$, with a focus on the connections between superconductivity,
magnetism, and electronic nematicity. The
BaFe$_{2}$(As$_{1-x}$P$_{x})_{2}$ (P:Ba122) system in particular has
received attention because isovalent substitution of As for P generates less
disorder than doping on the Fe site. The phase diagram of P:Ba122 is
characterized by a line of simultaneous antiferromagnetic (AF) and
tetragonal-to-orthorhombic transitions, $T_{s}(x)$, that penetrates the
superconducting dome at x$=$0.28, just below optimal doping
($x_{opt}=$0.30). In this work, we use spatially-resolved optical
polarimetry and photomodulated reflectance to detect linear birefringence
and therefore breaking of 4-fold rotational (C$_{4})$ symmetry. In
underdoped ($x$\textless 0.28) samples, birefringence appears at $T $\textgreater
$T_{s} $and grows continuously with decreasing $T$ . The birefringence is
unidirectional in a large (300 $\mu $m x300 $\mu $m) field of view,
suggesting that C$_{4}_{\, }$breaking in this range of $T$ is caused by
residual strain that couples to a diverging nematic susceptibility.
Birefringence maps just below $T_{s}(x)$ show the appearance of domains,
indicating the onset of spontaneous symmetry breaking to an AF ground state.
Surprisingly, in samples with $x$\textgreater 0.28, in which the low $T$ phase is
superconducting/ tetragonal rather than AF/orthorhombic, C$_{4}_{\,
}$breaking is observed as well, with an abrupt onset and domain formation at
55 K. We tentatively associate these features with a transition to an AF
phase induced by residual strain, as previously proposed [H.-H. Kuo et al.
Phys. Rev. B86, 134507 (2012)] to account for structure in resistivity vs.
$T$. Time-resolved photomodulation allow us to follow the amplitude of the AF
order with time following pulsed photoexcitation. Below $T_{c}$ the AF order
at first weakens , but then strengthens in response to the photoinduced
weakening of superconductivity. This complex time evolution is accounted for
quantitatively by a model based on the coexistence and competition of AF and
superconducting order.
*We gratefully acknowledge support by the U.S. Department of Energy, Office of Science, Materials Sciences and Engineering Division, and the Gordon and Betty Moore Foundation’s EPiQS Initiative through Grant GBMF4537.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2016.MAR.V1.5