[Paper Review] Growth and Anisotropy in transport properties and susceptibility of single crystals $BaFe_2As_2$

XueLiang Wang, Tao Wu+7 more|arXiv (Cornell University)|Jun 15, 2008

Iron-based superconductors research1 citations

TL;DR

This study presents intrinsic transport and magnetic properties of high-quality single crystals of BaFe₂As₂ grown via the self-flux method. It reveals a large resistivity anisotropy (~150) and field-dependent resistivity minima, with a log(1/T) divergence at low temperatures, indicating strong electron correlations. The absence of Curie-Weiss behavior and linear-in-T susceptibility above the SDW transition suggest local moments coexisting with itinerant electrons, akin to chromium’s SDW state.

ABSTRACT

Sizable single crystals of $BaFe_2As_2$ have been grown with self-flux method. The crystals are plate-like with c-axis perpendicular to the plane. The size can be as large as 3 x 5 x 0.2 $mm^3$. The resistivity anisotropy ($ ho_c/ ho_{ab}$) is as large as about 150, and independent of temperature. The transport in ab plane and along c-axis direction shares the same scattering mechanism. In contrast to the magnetic behavior of polycrystalline samples, no Curie-Weiss behavior are observed, a temperature linear dependent susceptibility occurs above spin-density-wave (SDW) transition. The susceptibility behavior is very similar to that of antiferromagnetic SDW chromium. Magnetic behavior of single crystal definitely gives evidence for existence of local moment except for the contribution to susceptibility from itinerant electrons. A resistivity minimum strongly dependent on magnetic field is observed. A log(1/T) divergency, similar to that of the underdoped cuprates, happens at low temperature. Here we first present intrinsic transport and magnetic properties, and their anisotropy from high quality single crystal.

Motivation & Objective

• To grow high-quality single crystals of BaFe₂As₂ using the self-flux method for intrinsic property measurements.
• To investigate the intrinsic anisotropy in electrical transport and magnetic susceptibility in single crystals.
• To resolve discrepancies between polycrystalline and single-crystal magnetic behavior, particularly regarding Curie-Weiss behavior and local moments.
• To examine the origin of low-temperature resistivity anomalies and their field dependence.
• To clarify the role of local moments versus itinerant electrons in the magnetic response above the SDW transition.

Proposed method

• Growth of plate-like BaFe₂As₂ single crystals using the self-flux method, achieving sizes up to 3 × 5 × 0.2 mm³ with c-axis perpendicular to the plane.
• Measurement of electrical resistivity along the ab-plane and c-axis to determine anisotropy (ρc/ρab ≈ 150) and identify common scattering mechanisms.
• Magnetic susceptibility measurements above the spin-density wave (SDW) transition to assess temperature dependence and compare with polycrystalline data.
• Analysis of field-dependent resistivity to detect minima and correlate with electronic correlations.
• Examination of low-temperature resistivity behavior for log(1/T) divergence, characteristic of underdoped cuprates.
• Use of single-crystal data to disentangle contributions from local moments and itinerant electrons in magnetic response.

Experimental results

Research questions

• RQ1 What is the intrinsic resistivity anisotropy in BaFe₂As₂ single crystals, and is it temperature-dependent?
• RQ2 How does the magnetic susceptibility of single crystals differ from that of polycrystalline samples above the SDW transition?
• RQ3 What evidence exists for local moments in BaFe₂As₂, and how do they contribute to the magnetic susceptibility?
• RQ4 Why is a resistivity minimum observed under magnetic field, and what does it reveal about electronic correlations?
• RQ5 Does the low-temperature resistivity exhibit log(1/T) divergence, and what does this imply about the electronic state?

Key findings

• The resistivity anisotropy (ρc/ρab) reaches ~150 and remains temperature-independent, indicating strong electronic anisotropy.
• The transport behavior along both ab-plane and c-axis follows the same scattering mechanism, suggesting a common scattering origin.
• No Curie-Weiss behavior is observed in single crystals above the SDW transition, contrasting with polycrystalline samples.
• A linear-in-T temperature dependence of magnetic susceptibility is observed above the SDW transition, similar to antiferromagnetic chromium.
• The magnetic response provides clear evidence for local moments, distinct from contributions by itinerant electrons.
• A resistivity minimum strongly dependent on magnetic field is observed, indicating field-tuned electronic correlations.
• A log(1/T) divergence in resistivity at low temperatures is observed, a hallmark of underdoped cuprate-like behavior.