A low temperature nonlinear optical rotational anisotropy spectrometer for the determination of crystallographic and electronic symmetries

Abstract

Nonlinear optical generation from a crystalline material can reveal the symmetries of both its lattice structure and underlying ordered electronic phases and can therefore be exploited as a complementary technique to diffraction based scattering probes. Although this technique has been successfully used to study the lattice and magnetic structures of systems such as semiconductor surfaces, multiferroic crystals, magnetic thin films and multilayers, challenging technical requirements have prevented its application to the plethora of complex electronic phases found in strongly correlated electron systems. These requirements include an ability to probe small bulk single crystals at the micron length scale, a need for sensitivity to the entire nonlinear optical susceptibility tensor, oblique light incidence reflection geometry and incident light frequency tunability among others. These measurements are further complicated by the need for extreme sample environments such as ultra low temperatures, high magnetic fields or high pressures. In this review we present a novel experimental construction using a rotating light scattering plane that meets all the aforementioned requirements. We demonstrate the efficacy of our scheme by making symmetry measurements on a micron scale facet of a small bulk single crystal of Sr 2 IrO 4 using optical second and third harmonic generation.

Structural investigation of the bilayer iridateSr3Ir2O7

“…These data were acquired using the rotating scattering plane based technique described in Ref. [35] from cleaved surfaces of Sr 3 Ir 2 O 7 with the long cell axis parallel to the surface normal. Incident light was provided by a Ti:sapph regenerative amplifier (800 nm center wavelength, 60 fs pulse duration, 10 kHz repetition rate) and focused to a spot size less than 100 µm on the crystal with a fluence less than 1 mJ/cm 2 .…”

High-speed measurement of rotational anisotropy nonlinear optical harmonic generation using position-sensitive detection

“…It also precludes the accurate measurement of temporal changes in the RA-NHG response of a sample that occurs on the timescale of a ϕ rotation period, which may arise from processes such as charge migration or impurity adsorption on the sample surface under vacuum conditions [23,24]. In this Letter, we demonstrate a novel high-speed RA-NHG setup using a position-sensitive detector that rotates ϕ at a frequency 10 3 to 10 4 times higher than conventional methods [21], which can in principle be increased to even higher frequencies.…”

“…An alternative approach in which the scattering plane is rotated while the sample is kept fixed has also recently been demonstrated, which is advantageous when studying small samples and when low temperatures or externally applied fields (e.g., magnetic, electric, strain) are desired [21,22]. In both methods, ϕ is stepped and held at discrete values for a finite wait time while the high-harmonic intensity is recorded.…”

Nonlinear and time-resolved optical study of the 112-type iron-based superconductor parentCa1−xLaxFeAs2across its structural phase transition

“…It can therefore be challenging to detect minute changes in symmetry from such techniques. Rotational anisotropy secondharmonic generation (RA-SHG) is an alternative method that relies on carefully measuring the tensor optical response of a crystal in order to determine the crystallographic and electronic point-group symmetries of solids [18,19]. As illustrated in Fig.…”