Abstract-Optical Kerr nonlinearity and multi-photon absorption of DSTMS measured by Z-scan method

 

Jiang Li, Rakesh Rana, Liguo Zhu, Cangli Liu, Harald Schneider, Alexej Pashkin

 https://arxiv.org/abs/2102.03242

We investigate the optical Kerr nonlinearity and multi-photon absorption (MPA) properties of DSTMS excited by femtosecond pulses at a wavelengths of 1.43 {\mu}m, which is optimal for terahertz generation via difference frequency mixing. The MPA and the optical Kerr coefficients of DSTMS at 1.43 {\mu}m are strongly anisotropic indicating a dominating contribution from cascaded 2nd-order nonlinearity. These results suggest that the saturation of the THz generation efficiency is mainly related to the MPA process and to a spectral broadening caused by cascaded 2nd-order frequency mixing within DSTMS

Abstract-Nonlinear Charge Transport in InGaAs Nanowires at Terahertz Frequencies

Rakesh Rana, Leila Balaghi, Ivan Fotev, Harald Schneider, Manfred Helm, Emmanouil Dimakis, Alexej Pashkin

https://arxiv.org/abs/2004.00484

We probe the electron transport properties in the shell of GaAs/In0.2Ga0.8As core/shell nanowires at high electric fields using optical pump / THz probe spectroscopy with broadband THz pulses and peak electric fields up to 0.6 MV/cm. The plasmon resonance of the photoexcited charge carriers exhibits a systematic redshift and a suppression of its spectral weight for THz driving fields exceeding 0.4 MV/cm. This behavior is attributed to the intervalley electron scattering resulting in the increase of the average electron effective mass and the corresponding decrease of the electron mobility by about 2 times at the highest fields. We demonstrate that the increase of the effective mass is non-uniform along the nanowires and takes place mainly in their middle part, leading to a spatially inhomogeneous carrier response. Our results quantify the nonlinear transport regime in GaAs-based nanowires and show their high potential for development of nano-devices operating at THz frequencies.

Abstract-Probing low energy dynamics in charge-ordered NdNiO3 by terahertz time domain spectroscopy

Sarmistha Das, Gulloo Lal Prajapati,  Rakesh Rana, Dhanvir Singh Rana

https://www.sciencedirect.com/science/article/pii/S0042207X17318584

Herein, we have investigated terahertz (THz) optical properties of high quality NdNiO₃epitaxial thin film deposited on pseudocubic NdGaO₃ (001) substrate. The detailed X-ray diffraction (XRD) characterizations reveal that the film possesses orthorhombic distortion in tensile strained state, induced by the substrate. Furthermore, a clearly discernible and well defined peak appeared in the real part of THz optical conductivity (σ₁) at the low temperature charge-ordered insulating phase. The peak gradually shifted to the higher frequency as the temperature increases and eventually disappears at 120 K. The presence of this peak only at the low temperature charge-ordered phase having Fermi surface nesting in the distorted structure clearly points towards its origin of the charge density wave (CDW) excitations in NdNiO₃.

Abstract-Terahertz spectroscopic evidence of low-energy excitations in NdNi O 3

Rakesh Rana, Parul Pandey, V. Eswara Phanindra, S. S. Prabhu, and D. S. Rana

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.97.045123

The charge-density waves (CDW) in the framework Landau theory are visualized to manifest in complex $R\mathrm{Ni}{O}_3$ ($R$ = rare-earth) nickelates in which the structure controls the incipient charge order in the weak localization limit. Any consequent effect demonstrating these nickelates in the rare category of CDW conductors with controlled charge-lattice interactions has been elusive so far. Employing terahertz time-domain spectroscopy along selective crystal axes, we present evidence of the CDW in epitaxial strain-modulated crystal structures of prototypical $\mathrm{NdNi}{O}_3$. A finite peak structure at 5 meV in the terahertz conductivity displays all the characteristics of a CDW condensate in (110)- and (111)-oriented $\mathrm{NdNi}{O}_3$ thin films. Contrasting charge dynamics of collective CDW mode and Drude conductivity emerging across dissimilar orientations helps disentangle charge ordering from the metal-insulator transition and establish a structure-property cause-effect relationship which may propose novel attributes in emerging oxide electronics.

• 
• 
• 
• 
• 
• 

Abstract-Tuning the terahertz low-energy charge dynamics by simultaneous effect of epitaxial and anisotropic strain in PrNi O 3 thin films

V. Eswara Phanindra, Sarmistha Das, K. Santhosh Kumar, Piyush Agarwal, Rakesh Rana, and D. S. Rana

Phys. Rev. B 95, 085114 – Published 13 February 2017

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.95.085114

The interplay of charge, spin, and lattice correlations strongly influence the insulator-metal (I-M) transition and magnetic ordering in rare earth nickelates. In this context, we explored the low-energy charge dynamics in structurally modulated $\mathrm{PrNi}{O}_3$ (PNO) thin films to unravel the complexity of ground state across I-M transition using terahertz (THz) spectroscopy. The THz optical constants of compressive film on $\mathrm{LaAl}{O}_3$ (100) substrate and the tensile films on $\mathrm{NdGa}{O}_3$ (100), (001), (110), and (111) substrates with varying orthorhombic distortion exhibit remarkably distinct features as a function of frequency and temperature. The THz conductivity of compressive film sans any I-M transition follows the Drude model. In contrast, the tensile strained films exhibit non-Drude THz conductivity, a giant positive dielectric permittivity, and negative imaginary conductivity, all of which can be explained by the Drude-Smith model. This rich variety of low-energy dynamics manifests as a function of temperature, strain, and crystal orientation. Such distinct THz spectral features, as induced by a subtle variation in strain while crossing over from tensile to compressive strain and with varying degree of orthorhombicity coupled with oxygen vacancies, reveal a novel facet of structure-property relationship of PNO.

• 
• 
• 
• 
• 
• 
• 

Abstract-Terahertz spectroscopy of PrNiO3 thin films: Strain induced anomalous conductivity, giant dielectric constant, and scaling of optical constants

V. Eswara Phanindra, Sarmistha Das, K. Santhosh Kumar, Piyush Agarwal, Rakesh Rana, and D. S. Rana

https://journals.aps.org/prb/accepted/d7072Ob8F5914b3750bc5439b7a764bc02ee8b8e5

The interplay of charge, spin, and lattice correlations strongly influence the insulator-metal (I-M) transition and magnetic ordering in rare earth nickelates. In this context, we explored the low-energy charge dynamics in structurally modulated PrNiO3 thin films to unravel the complexity of ground state across I-M transition using terahertz (THz) spectroscopy. The THz optical constants of compressive film on LaAlO3 (100) substrate and the tensile films on NdGaO3 (100), (001), (110) and (111) substrates with varying orthorhombic distortion exhibit remarkably distinct features as a function of frequency and temperature. The THz conductivity of compressive film sans any I-M transition follows the Drude model. In contrast, the tensile strained films exhibit non-Drude THz conductivity, a giant positive dielectric permittivity and negative imaginary conductivity, all of which can be explained by Drude-Smith model. This rich variety of low energy dynamics manifest as a function of temperature, strain and crystal orientation. Such distinct THz spectral features, as induced by a subtle variation in strain while crossing over from tensile to compressive strain and with varying degree of orthorhombicity coupled with oxygen vacancies, reveal a novel facet of structure-property relationship of PrNiO3.

Abstract-Observation and Structural Control of Charge-Density-Waves resonating with Terahertz Frequencies in NdNiO3

Rakesh Rana, Parul Pandey, S. S. Prabhu, D. S. Rana

(Submitted on 10 Dec 2014)

http://arxiv-web3.library.cornell.edu/abs/1412.3244

Formation of charge-density-waves in ordered electronic phases (such as charge-order) is an emergent phenomenon in the perovskite class of correlated oxides. This scenario is visualized to prevail in exotic RNiO3 (R=rare-earth) nickelates in which the structure controls the incipient charge-order to form in weak localization limit. However, any consequent effect demonstrating these nickelates in rare category of charge-density-waves conductors with controlled charge-lattice interactions has been a fundamental challenge so-far. Here, we present first evidence of the charge-density-waves in a prototypical NdNiO3 system employing terahertz time-domain spectroscopy along selective crystal axes. A finite peak structure at 5meV in the terahertz conductivity displays all the characteristics of a charge-density-wave condensate. Contrasting charge-dynamics of collective charge-density-waves mode and Drude conductivity emerging, respectively, from orthorhombic and cubic symmetries disentangle charge-ordering from the insulating state, establish a novel structure-property cause-effect relationship, and present opportunities to harness these diverse attributes in oxide electronics.

Subjects:	Strongly Correlated Electrons (cond-mat.str-el)
Cite as:	arXiv:1412.3244 [cond-mat.str-el]
	(or arXiv:1412.3244v1 [cond-mat.str-el] for this version)

Submission history

From: Rakesh Rana [view email]
[v1] Wed, 10 Dec 2014 10:12:40 GMT (1766kb)