[Paper Review] Spectral evolution in a Shastry-Sutherland lattice, HoB(4)

Deepnarayan Biswas, Nishaina Sahadev+3 more|arXiv (Cornell University)|Oct 31, 2013

Rare-earth and actinide compounds37 references3 citations

TL;DR

This study investigates the electronic structure of HoB4, a non-collinear Shastry-Sutherland lattice system, using high-resolution photoemission spectroscopy and ab initio band structure calculations. It reveals particle-hole asymmetry and a |ε−εF|⁰.⁵ dependence in the spectral function near the Fermi level, indicating disorder-induced effects similar to those in charge-disordered systems, with a sharp dip at 10 K signaling long-range antiferromagnetic order.

ABSTRACT

We studied the electronic structure of a Shastry-Sutherland lattice system, HoB4 employing high resolution photoemission spectroscopy and ab initio band structure calculations. The surface and bulk borons exhibit subtle differences, and loss of boron compared to the stoichiometric bulk. However, the surface and bulk conduction bands near Fermi level are found to be similar. Evolution of the electronic structure with temperature is found to be similar to that observed in a typical charge-disordered system. A sharp dip is observed at the Fermi level in the low temperature spectra revealing signature of antiferromagnetic gap. Asymmetric spectral weight transfer with temperature manifests particle-hole asymmetry that may be related to the exotic properties of these systems.

Motivation & Objective

• To investigate the electronic structure of HoB4, a rare-earth tetraboride with a Shastry-Sutherland lattice, under varying temperatures.
• To understand the role of spin disorder and electron correlation in shaping the electronic properties of this complex quantum material.
• To probe surface-bulk differences and the impact of boron deficiency on electronic structure.
• To determine whether spectral features near the Fermi level reflect charge disorder or magnetic correlations.

Proposed method

• High-resolution photoemission spectroscopy (PES) using Al Kα, He I, and He II radiation sources to probe valence and core levels.
• Angle-integrated and angle-resolved PES measurements at temperatures from 10 K to 300 K to study spectral evolution.
• Ab initio band structure calculations using the full potential linearized augmented plane wave (FP-LAPW) method within LDA and LDA+U approximations.
• Spectral weight transfer analysis via subtraction of spectra at 300 K from lower-temperature spectra to detect asymmetry.
• Symmetrization of spectra and division by Fermi-Dirac distribution to extract spectral density of states (SDOS).
• Use of WIEN2k software for electronic structure calculations with 1000 k-points in the first Brillouin zone and convergence criteria for charge and energy.

Experimental results

Research questions

• RQ1 How does the electronic structure of HoB4 evolve with temperature, and what does it reveal about many-body interactions?
• RQ2 To what extent do surface and bulk electronic structures in HoB4 differ, and how does boron deficiency affect them?
• RQ3 What causes the observed particle-hole asymmetry in the spectral weight transfer across the Fermi level?
• RQ4 Why does the spectral function near the Fermi level follow a |ε−εF|⁰.⁵ dependence, and what does this imply about the nature of electronic disorder?
• RQ5 What is the origin of the sharp dip at the Fermi level in the 10 K spectrum, and how is it related to magnetic ordering?

Key findings

• The surface and bulk valence bands near the Fermi level are similar, despite subtle differences and boron loss at the surface.
• A sharp dip at the Fermi level in the 10 K spectrum provides direct evidence of long-range antiferromagnetic order.
• Spectral weight transfer with temperature is asymmetric, with greater changes above the Fermi level, indicating particle-hole asymmetry.
• The spectral density of states near the Fermi level follows a |ε−εF|⁰.⁵ dependence, characteristic of charge-disorder effects as predicted by Altshuler-Aronov theory.
• The 2p orbital character dominates the spectral intensity near the Fermi level, indicating strong hybridization between Ho 4f and boron 2p states.
• The LDA+U calculation confirms the importance of electron correlation in Ho 4f electrons, with satellite features observed in Ho core-level spectra.