Chan, Julia Y.

Permanent URI for this collectionhttps://hdl.handle.net/10735.1/4226

Julia Chan is Professor of Solid State and Materials Chemistry in the Department of Chemistry and head of The Chan Lab. Dr. Chan's research "is focused on crystal growth, structure (X-ray and neutron), and characterization (electrical, magnetic, transport) of intermetallics and oxides for energy applications, including:

Highly correlated electronic materials
Magnetic frustrated materials
Search and discovery of intermetallics with low thermal conductivity"

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Elected Fellow of the American Association for the Advancement of Science (AAAS) in November 2019.

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Bulk Fermi Surface of The Weyl Type-II Semimetallic Candidate NbIrTe₄
(American Physical Society, 2019-05-15) Schönemann, R.; Chiu, Y. -C; Zheng, W.; Quito, V. L.; Sur, S.; McCandless, Gregory T.; Chan, Julia Y.; Balicas, L.; 0000-0003-4434-2160 (Chan, JY); McCandless, Gregory T.; Chan, Julia Y.
Recently, a new group of layered transition-metal tetra-chalcogenides was proposed via first-principles calculations to correspond to a new family of Weyl type-II semimetals with promising topological properties in the bulk as well as in the monolayer limit. In this paper, we present measurements of the Shubnikov-de Haas (SdH) and de Haas-van Alphen effects under high magnetic fields for the type-II Weyl semimetallic candidate NbIrTe₄. We find that the angular dependence of the observed Fermi surface extremal cross-sectional areas agree well with our density functional theory (DFT) calculations supporting the existence of Weyl type-II points in this material. Although we observe a large and nonsaturating magnetoresistivity in NbIrTe4 under fields all the way up to 35T, Hall-effect measurements indicate that NbIrTe₄ is not a compensated semimetal. The transverse magnetoresistivity displays a fourfold angular dependence akin to the so-called butterfly magnetoresistivity observed in nodal line semimetals. We conclude that the magnetoresistivity and its unconventional angular dependence are governed by the topography of the Fermi surface and the resulting anisotropy in effective masses and in carrier mobilities. © 2019 American Physical Society.
Detailed Study of the Fermi Surfaces of the Type-II Dirac Semimetallic Candidates XTe₂ (X =Pd, Pt)
(American Physical Society) Zheng, W.; Schönemann, R.; Aryal, N.; Zhou, Q.; Rhodes, D.; Chiu, Y. -C; Chen, K. -W; Kampert, E.; Förster, T.; Martin, T. J.; McCandless, Gregory T.; Chan, Julia Y.; Manousakis, E.; Balicas, L.; 0000-0003-4434-2160 (Chan, JY); Martin, T. J.; McCandless, Gregory T.; Chan, Julia Y.
We present a detailed quantum oscillatory study on the Dirac type-II semimetallic candidates PdTe₂ and PtTe₂ via the temperature and the angular dependence of the de Haas-van Alphen and Shubnikov-de Haas effects. In high-quality single crystals of both compounds, i.e., displaying carrier mobilities between 10³ and 10⁴ cm²/Vs, we observed a large nonsaturating magnetoresistivity which in PtTe₂ at a temperature T=1.3 K leads to an increase in the resistivity up to (5×10⁴)% under a magnetic field μ₀H=62 T. These high mobilities correlate with their light effective masses in the range of 0.04 to 1 bare electron mass according to our measurements. For PdTe₂ the experimentally determined Fermi surface cross-sectional areas show excellent agreement with those resulting from band structure calculations. Surprisingly, this is not the case for PtTe₂, whose agreement between calculations and experiments is relatively poor even when electronic correlations are included in the calculations. Therefore, our study provides strong support for the existence of a Dirac type-II node in PdTe₂ and probably also for PtTe₂. Band structure calculations indicate that the topologically nontrivial bands of PtTe₂ do not cross the Fermi level. In contrast, for PdTe₂ the Dirac type-II cone does intersect, although our calculations also indicate that the associated cyclotron orbit on the Fermi surface is located in a distinct k_z plane with respect to that of the Dirac type-II node. Therefore, it should yield a trivial Berry phase.
Emerging Investigators in Solid-State Inorganic Chemistry
(Amer Chemical Soc, 2018-12-10) Latturner, Susan E.; Chan, Julia Y.; 0000-0003-4434-2160 (Chan, JY); Chan, Julia Y.
No abstract available.
Fermi Surface of the Weyl Type-II Metallic Candidate WP₂
(2018-09-12) Schönemann, R.; Aryal, N.; Zhou, Q.; Chiu, Y. -C; Chen, K. -W; Martin, T. J.; McCandless, G. T.; Chan, Julia Y.; Manousakis, E.; Balicas, L.; Martin, T. J.; McCandless, G. T.; Chan, Julia Y.
Weyl type-II fermions are massless quasiparticles that obey the Weyl equation and which are predicted to occur at the boundary between electron and hole pockets in certain semimetals, i.e., the (W,Mo)(Te₁,P)₂ compounds. Here, we present a study of the Fermi surface of WP₂ via the Shubnikov-de Haas (SdH) effect. Compared to other semimetals, WP₂ exhibits a very low residual resistivity, i.e., ρ₀≃10 nΩ cm, which leads to perhaps the largest nonsaturating magnetoresistivity [ρ(H)] reported for any compound. For the samples displaying the smallest ρ₀, ρ(H) is observed to increase by a factor of 2.5×10⁷% under μ₀H=35 T at T=0.35 K. The angular dependence of the SdH frequencies is found to be in excellent agreement with the first-principles calculations when the electron and hole bands are shifted by 30 meV with respect to the Fermi level. This small discrepancy could have implications for the predicted topological character of this compound.
Fermi Surface, Possible Unconventional Fermions, and Unusually Robust Resistive Critical Fields in the Chiral-Structured Superconductor AuBe
(American Physical Society) Rebar, D. J.; Birnbaum, S. M.; Singleton, J.; Khan, M.; Ball, J. C.; Adams, P. W.; Chan, Julia Y.; Young, D. P.; Browne, D. A.; Ditusa, J. F.; 0000-0003-4434-2160 (Chan, JY); Chan, Julia Y.
The noncentrosymmetric superconductor (NCS) AuBe is investigated using a variety of thermodynamic and resistive probes in magnetic fields of up to 65 T and temperatures down to 0.3 K. Despite the polycrystalline nature of the samples, the observation of a complex series of de Haas-van Alphen (dHvA) oscillations has allowed the calculated band structure for AuBe to be validated. This permits a variety of BCS parameters describing the superconductivity to be estimated, despite the complexity of the measured Fermi surface. In addition, AuBe displays a nonstandard field dependence of the phase of dHvA oscillations associated with a band thought to host unconventional fermions in this chiral lattice. This result demonstrates the power of the dHvA effect to establish the properties of a single band despite the presence of other electronic bands with a larger density of states, even in polycrystalline samples. In common with several other NCSs, we find that the resistive upper critical field exceeds that measured by heat capacity and magnetization by a considerable factor. We suggest that our data exclude mechanisms for such an effect associated with disorder, implying that topologically protected superconducting surface states may be involved. ©2019 American Physical Society.
Ferromagnetic Ordering Along the Hard Axis in the Kondo Lattice YbIr₃Ge₇
(American Physical Society) Rai, B. K.; Stavinoha, M.; Banda, J.; Hafner, D.; Benavides, Katherine A.; Sokolov, D. A.; Chan, Julia Y.; Brando, M.; Huang, C. -L; Morosan, E.; Benavides, Katherine A.; Chan, Julia Y.
Ferromagnetic Kondo lattice compounds are far less common than their antiferromagnetic analogs. In this Rapid Communication, we report the discovery of a ferromagnetic Kondo lattice compound, YbIr₃Ge₇. As in almost all ferromagnetic Kondo lattice systems, YbIr₃Ge₇ shows magnetic order with moments aligned orthogonal to the crystal electric field (CEF) easy axis. YbIr₃Ge₇ is unique in that it is the only member of this class of compounds that crystallizes in a rhombohedral structure with a trigonal point symmetry of the magnetic site, and it lacks broken inversion symmetry at the local moment site. The ac magnetic susceptibility, magnetization, and specific heat measurements show that YbIr₃Ge₇ has a Kondo temperature TK≈14 K and a Curie temperature T_{C}=2.4K. Ferromagnetic order occurs along the crystallographic [100] hard CEF axis despite the large CEF anisotropy of the ground-state Kramers doublet with a saturation moment along [001] almost four times larger than the one along [100]. This implies that a mechanism which considers the anisotropy in the exchange interaction to explain the hard-axis ordering is unlikely. On the other hand, the broad second-order phase transition at T_{C} favors a fluctuation-induced mechanism. © 2019 American Physical Society.
Hydrostatic Pressure-Induced Modifications of Structural Transitions Lead to Large Enhancements of Magnetocaloric Effects in MnNiSi-Based Systems
(Amer Physical Soc, 2015-01-05) Samanta, Tapas; Lepkowski, Daniel L.; Saleheen, Ahmad Us; Shankar, Alok; Prestigiacomo, Joseph; Dubenko, Igor; Quetz, Abdiel; Oswald, Iain W. H.; McCandless, Gregory T.; Chan, Julia Y.; Adams, Philip W.; Young, David P.; Ali, Naushad; Stadler, Shane
A remarkable decrease of the structural transition temperature of MnNiSi from 1200 to < 300 K by chemically alloying it with MnFeGe results in a coupling of the magnetic and structural transitions, leading to a large magnetocaloric effect near room temperature. Application of relatively low hydrostatic pressures (similar to 2.4 kbar) lead to an extraordinary enhancement of the isothermal entropy change from -Delta S = 44 to 89 J/kgK at ambient and 2.4 kbar applied pressures, respectively, for a field change of Delta B = 5 T, and is associated with a large relative volume change of about 7% with P = 2.4 kbar.
Intermediate Valence to Heavy Fermion Through a Quantum Phase Transition in Yb₃(Rh₁₋xTx)₄ Ge₁₃ (T = Co, Ir) Single Crystals
(Amer Physical Soc, 2016-01-04) Rai, Binod K.; Oswald, Iain W. H.; Chan, Julia Y.; Morosan, E.; Oswald, Iain W. H.; Chan, Julia Y.
Single crystals of Yb₃(Rh₁₋xTx)₄ Ge₁₃ (T = Co, Ir) have been grown using the self-flux method. Powder x-ray diffraction data on these compounds are consistent with the cubic structure with space group Pm3̅n. Intermediate-valence behavior is observed in Yb₃(Rh₁₋xTx)₄ Ge₁₃ upon T = Co doping, while T = Ir doping drives the system into a heavy-fermion state. Antiferromagnetic order is observed in the Ir-doped samples Yb₃(Rh₁₋xTx)₄ Ge₁₃ for 0.5 < x ≤ 1 with T_N = 0.96 K for Yb₃Ir₄Ge₁₃. With decreasing x, the magnetic order is suppressed towards a quantum critical point around x_c = 0.5, accompanied by non-Fermi-liquid behavior evidenced by logarithmic divergence of the specific heat and linear temperature dependence of the resistivity. The Fermi-liquid behavior is recovered with the application of large magnetic fields.
Law and Disorder: Special Stacking Units—Building the Intergrowth Ce₆ Co₅ Ge₁₆
(American Chemical Society, 2019-04-22) Felder, Justin B.; Weiland, Ashley; Hodovanets, H.; McCandless, George T.; Estrada, Tania G.; Martin, Thomas J.; Walker, Amy V.; Paglione, J.; Chan, Julia Y.; 0000-0003-4434-2160 (Chan, JY); 0000-0002-2528-1967 (Felder, JB); 0000-0001-7198-3559 (Weiland, A); 0000-0003-2114-3644 (Walker, AV); Felder, Justin B.; Weiland, Ashley; McCandless, George T.; Estrada, Tania G.; Martin, Thomas J.; Walker, Amy V.; Chan, Julia Y.
A new structure type of composition Ce₆ Co₅ Ge₁₆ was grown out of a molten Sn flux. Ce₆ Co₅ Ge₁₆ crystallizes in the orthorhombic space group Cmcm, with highly anisotropic lattice parameters of α = 4.3293(5) Å, b = 55.438(8) Å, and c = 4.3104(4) Å. The resulting single crystals were characterized by X-ray diffraction, and the magnetic and transport properties are presented. The Sn-stabilized structure of Ce₆ Co₅ Ge₁₆ is based on the stacking of disordered Ce cuboctahedra and is an intergrowth of existing structure types including AlB₂ , BaNiSn₃, and AuCu₃. The stacking of structural subunits has previously been shown to be significant in the fields of superconductivity, quantum materials, and optical materials. Herein, we present the synthesis, characterization, and complex magnetic behavior of Ce₆ Co₅ Ge₁₆ at low temperature, including three distinct magnetic transitions. © 2019 American Chemical Society.
Magnetic, Thermodynamic, and Electrical Transport Properties of the Noncentrosymmetric B20 Germanides MnGe and CoGe
(American Physical Society, 2014-10-03) Ditusa, J. F.; Zhang, S. B.; Yamaura, K.; Xiong, Y.; Prestigiacomo, J. C.; Fulfer, B. W.; Adams, P. W.; Brickson, M. I.; Browne, D. A.; Capan, C.; Fisk, Z.; Chan, Julia Y.; C-5392-2008 (Chan, JY)
We present magnetization, specific heat, resistivity, and Hall effect measurements on the cubic B20 phase of MnGe and CoGe and compare to measurements of isostructural FeGe and electronic-structure calculations. In MnGe, we observe a transition to a magnetic state at Tc=275K as identified by a sharp peak in the ac magnetic susceptibility, as well as second phase transition at lower temperature that becomes apparent only at finite magnetic field. We discover two phase transitions in the specific heat at temperatures much below the Curie temperature, one of which we associate with changes to the magnetic structure. A magnetic field reduces the temperature of this transition which corresponds closely to the sharp peak observed in the ac susceptibility at fields above 5 kOe. The second of these transitions is not affected by the application of field and has no signature in the magnetic properties or our crystal-structure parameters. Transport measurements indicate that MnGe is metallic with a negative magnetoresistance similar to that seen in isostructural FeGe and MnSi. Hall effect measurements reveal a carrier concentration of about 0.5 carriers per formula unit, also similar to that found in FeGe and MnSi. CoGe is shown to be a low carrier density metal with a very small, nearly temperature-independent diamagnetic susceptibility.
Observation of a Two-Dimensional Fermi Surface and Dirac Dispersion in YbMnSb₂
(Amer Physical Soc, 2018-10-22) Kealhofer, Robert; Jang, Sooyoung; Griffin, Sinead M.; John, Caolan; Benavides, Katherine A.; Doyle, Spencer; Helm, T.; Moll, Philip J. W.; Neaton, Jeffrey B.; Chan, Julia Y.; Denlinger, J. D.; Analytis, James G.; 0000-0003-4434-2160 (Chan, JY); Benavides, Katherine A.; Chan, Julia Y.
We present the crystal structure, electronic structure, and transport properties of the material YbMnSb₂, a candidate system for the investigation of Dirac physics in the presence of magnetic order. Our measurements reveal that this system is a low-carrier-density semimetal with a two-dimensional Fermi surface arising from a Dirac dispersion, consistent with the predictions of density-functional-theory calculations of the antiferromagnetic system. The low temperature resistivity is very large, suggesting that scattering in this system is highly efficient at dissipating momentum despite its Dirac-like nature.
One-Dimensional Tellurium Chains: Crystal Structure and Thermodynamic Properties of PrCuₓTe₂ (x ~ 0.45)
(Elsevier Inc., 2018-10-20) Baumbach, Ryan; Balicas, Luis; McCandless, Gregory T.; Sotelo, Paola; Zhang, Qiu R.; Evans, Jess; Camdzic, Dino; Martin, Thomas J.; Chan, Julia Y.; Macaluso, Robin T.; 0000-0003-4434-2160 (Chan, JY); McCandless, Gregory T.; Martin, Thomas J.; Chan, Julia Y.
X-ray diffraction, crystal structure, magnetization, and heat capacity results are presented for the rare earth chalcogenide ternary system PrCu₀.₄₅Te₂ and its non-4⨍ analogue LaCu₀.₄₀Te₂. The crystal structure of PrCu₀.₄₅Te₂ is characterized by chains of edge and corner-sharing CuTe₄ tetrahedra and Pr centered in polyhedra comprised of Cu and Te. The Cu site is partially occupied and exhibits signatures of local disorder. Magnetic susceptibility measurements show a Curie-Weiss temperature dependence consistent with a Pr³⁺ state. No magnetic ordering is observed down to 1.8 K, but the negative Curie-Weiss temperature suggests an antiferromagnetic exchange interaction. Importantly, the low temperature heat capacity of PrCu₀.₄₅Te₂ is strongly enhanced by comparison to LaCu₀.₄₀Te₂, suggesting that there is a build-up of entropy that is associated with the 4f-electrons from the Pr³⁺ ions. These features reveal possible spin frustration behavior and introduce this family of materials as a template for studying new phenomenon.
The Proof Is in the Powder: Revealing Structural Peculiarities in the Yb₃Rh₄Sn₁₃ Structure Type
(Royal Soc Chemistry, 2018-09-12) Oswald, Iain W. H.; Rai, Binod K.; McCandless, Gregory T.; Morosan, Emilia; Chan, Julia Y.; 0000-0003-4434-2160 (Chan, JY); Oswald, Iain W. H.; Rai, Binod K.; McCandless, Gregory T.; Morosan, Emilia; Chan, Julia Y.
Compounds adopting the Yb₃Rh₄Sn₁₃ structure type have drawn attention because of the revelation of exotic states such as heavy fermion behavior, superconductivity, charge density wave, and quantum critical behavior. The prototypical structure has historically been modeled with a primitive cubic space group, Pm3̅n; however, structural studies have led to the realization of disordered atomic sites, requiring lower symmetry models. We will review the low symmetry models required to describe the structural distortions in the related Yb₃Rh₄Sn₁₃ structure type. In addition, we present the structure determination of a new analogue, Lu₃Ir₄Ge₁₃, which adopts a new structural model in /4₁/amd.
The Role of Ceramic and Glass Science Research in Meeting Societal Challenges: Report from an NSF-Sponsored Workshop
(Wiley, 2018-08-20) Faber, Katherine T.; Asefa, Tewodros; Backhaus-Ricoult, Monika; Brow, Richard; Chan, Julia Y.; Dillon, Shen; Fahrenholtz, William G.; Finnis, Michael W.; Garay, Javier E.; Garcia, R. Edwin; Gogotsi, Yury; Haile, Sossina M.; Halloran, John; Hu, Juejun; Huang, Liping; Jacobsen, Steven D.; Lara-Curzio, Edgar; LeBeau, James; Lee, William E.; Levi, Carlos G.; Levin, Igor; Lewis, Jennifer A.; Lipkin, Don M.; Lu, Kathy; Luo, Jian; Maria, Jon-Paul; Martin, Lane W.; Martin, Steve; Messing, Gary; Navrotsky, Alexandra; Padture, Nitin P.; Randall, Clive; Rohrer, Gregory S.; Rosenflanz, Anatoly; Schaedler, Tobias A.; Schlom, Darrell G.; Sehirlioglu, Alp; Stevenson, Adam J.; Tani, Toshihiko; Tikare, Veena; Trolier-McKinstry, Susan; Wang, Hong; Yildiz, Bilge; 0000-0003-4434-2160 (Chan, JY); Chan, Julia Y.
Under the sponsorship of the U.S. National Science Foundation, a workshop on emerging research opportunities in ceramic and glass science was held in September 2016. Reported here are proceedings of the workshop. The report details eight challenges identified through workshop discussions: Ceramic processing: Programmable design and assembly; The defect genome: Understanding, characterizing, and predicting defects across time and length scales; Functionalizing defects for unprecedented properties; Ceramic flatlands: Defining structure-property relations in free-standing, supported, and confined two-dimensional ceramics; Ceramics in the extreme: Discovery and design strategies; Ceramics in the extreme: Behavior of multimaterial systems; Understanding and exploiting glasses and melts under extreme conditions; and Rational design of functional glasses guided by predictive modeling. It is anticipated that these challenges, once met, will promote basic understanding and ultimately enable advancements within multiple sectors, including energy, environment, manufacturing, security, and health care.
Spin Density Wave Instability in a Ferromagnet
(Nature Publishing Group) Wu, Yan; Ning, Zhenhua; Cao, Huibo; Cao, Guixin; Benavides, Katherine A.; Karna, S.; McCandless, Gregory T.; Jin, R.; Chan, Julia Y.; Shelton, W. A.; DiTusa, J. F.; McCandless, Gregory T.; Chan, Julia Y.
Due to its cooperative nature, magnetic ordering involves a complex interplay between spin, charge, and lattice degrees of freedom, which can lead to strong competition between magnetic states. Binary Fe₃Ga₄ is one such material that exhibits competing orders having a ferromagnetic (FM) ground state, an antiferromagnetic (AFM) behavior at intermediate temperatures, and a conspicuous re-entrance of the FM state at high temperature. Through a combination of neutron diffraction experiments and simulations, we have discovered that the AFM state is an incommensurate spin-density wave (ISDW) ordering generated by nesting in the spin polarized Fermi surface. These two magnetic states, FM and ISDW, are seldom observed in the same material without application of a polarizing magnetic field. To date, this unusual mechanism has never been observed and its elemental origins could have far reaching implications in many other magnetic systems that contain strong competition between these types of magnetic order. Furthermore, the competition between magnetic states results in a susceptibility to external perturbations allowing the magnetic transitions in Fe3Ga4 to be controlled via temperature, magnetic field, disorder, and pressure. Thus, Fe₃Ga₄ has potential for application in novel magnetic memory devices, such as the magnetic components of tunneling magnetoresistance spintronics devices.
The Role of Crystal Growth Conditions on the Magnetic Properties of Ln₂Fe₄₋ₓCoₓSb₅ (Ln = La and Ce)
(American Chemical Society, 2019-04-15) Weiland, Ashley; Li, Sheng; Benavides, Katherine A.; Burnett, Joseph V.; Milam-Guerrero, J.; Neer, Abbey J.; McCandless, Gregory T.; Lv, Bing; Chan, Julia Y.; 0000-0001-7198-3559 (Weiland, A); 0000-0002-9491-5177 (Lv, B); 0000-0003-4434-2160 (Chan, JY); Weiland, Ashley; Li, Sheng; Benavides, Katherine A.; Burnett, Joseph V.; Neer, Abbey J.; McCandless, Gregory T.; Lv, Bing; Chan, Julia Y.
Single crystals of Ln₂Fe₄₋ₓCoₓSb_{5-y}Bi_y (Ln = La, Ce; 0 ≤ x ≤ 0.5; 0 ≤ y ≤ 0.2) were grown using Bi flux and self-flux methods. The compounds adopt the La₂Fe₄Sb₅ structure type with tetragonal space group I4/mmm. The La₂Fe₄Sb₅ structure type is comprised of rare earth atoms capping square Sb nets in a square antiprismatic fashion and two transition-metal networks forming a PbO-type layer with Sb and transition-metal isosceles triangles. Substituting Co into the transition-metal sublattice results in a decrease in the transition temperature and reduced frustration, indicative of a transition from localized to itinerant behavior. In this manuscript, we demonstrated that Bi can be used as an alternate flux to grow single crystals of antimonides. Even with the incorporation of Bi into the Sb square net, the magnetic properties are not significantly affected. In addition, we have shown that the incorporation of Co into the Fe triangular sublattice leads to an itinerant magnetic system. ©2019 American Chemical Society.

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